11:04 p.m.
At the moment, guests that are backed by hugepages in the host are
only able to use policy to control the placement of those hugepages
on a per-(guest-)CPU basis. Policy applied globally is ignored.
Such guests would use <memoryBacking><hugepages/></memoryBacking> and
a <numatune> block with <memory mode=... nodeset=.../> but no <memnode
.../> elements.
This patch corrects this by, in this specific case, changing the QEMU
command line from "-mem-prealloc -mem-path=..." (which cannot
specify NUMA policy) to "-object memory-backend-file ..." (which can).
Note: This is not visible to the guest and does not appear to create
a migration incompatibility.
Signed-off-by: Sam Bobroff <sam.bobroff(a)au1.ibm.com>
---
There was some discussion leading up to this patch, here:
https://www.redhat.com/archives/libvir-list/2016-October/msg00033.html
During that discussion it seemed that fixing this issue would cause
migration incompatibility but after some careful testing, it appears
that it only does when a memory-backend object is attached to a guest
NUMA node and that is not the case here. If only one is created, and
used globally (not attached via mem=<id>), the migration data does not
seem to be changed and so it seems reasonable to try something like
this patch.
This patch does work for my test cases but I don't claim a deep
understanding of the libvirt code so this is at least partly a RFC.
Comments welcome :-)
Cheers,
Sam.
src/qemu/qemu_command.c | 55 ++++++++++++++++++++++++++++++++++++++++---------
src/qemu/qemu_command.h | 2 +-
2 files changed, 46 insertions(+), 11 deletions(-)
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 0804133..c28c8f2 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3143,7 +3143,7 @@ qemuBuildMemoryBackendStr(unsigned long long size,
int guestNode,
virBitmapPtr userNodeset,
virBitmapPtr autoNodeset,
- virDomainDefPtr def,
+ const virDomainDefPtr def,
virQEMUCapsPtr qemuCaps,
virQEMUDriverConfigPtr cfg,
const char **backendType,
@@ -7129,12 +7129,18 @@ qemuBuildSmpCommandLine(virCommandPtr cmd,
static int
qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
- const virDomainDef *def,
+ const virDomainDefPtr def,
virQEMUCapsPtr qemuCaps,
- virCommandPtr cmd)
+ virCommandPtr cmd,
+ virBitmapPtr auto_nodeset)
{
const long system_page_size = virGetSystemPageSizeKB();
char *mem_path = NULL;
+ virBitmapPtr nodemask = NULL;
+ const char *backendType = NULL;
+ char *backendStr = NULL;
+ virJSONValuePtr props;
+ int rv = -1;
/*
* No-op if hugepages were not requested.
@@ -7159,18 +7165,47 @@ qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
if (qemuGetHupageMemPath(cfg, def->mem.hugepages[0].size, &mem_path) < 0)
return -1;
- virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path", mem_path,
NULL);
+ if (virDomainNumatuneMaybeGetNodeset(def->numa, auto_nodeset,
+ &nodemask, -1) < 0)
+ return -1;
+ if (nodemask && virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE)) {
+ props = virJSONValueNewObject();
+ if (qemuBuildMemoryBackendStr(virDomainDefGetMemoryInitial(def),
+ 0, -1, NULL, auto_nodeset,
+ def, qemuCaps, cfg, &backendType,
+ &props, false) < 0)
+ goto cleanup;
+ if (!(backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType,
+ "mem",
+ props)))
+ goto cleanup;
+ virCommandAddArgList(cmd, "-object", backendStr, NULL);
+ rv = 0;
+cleanup:
+ VIR_FREE(backendStr);
+ VIR_FREE(props);
+ }
+ else {
+ if (nodemask || 1)
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("Memory file backend objects are "
+ "unsupported by QEMU binary. Global NUMA "
+ "hugepage policy will be ignored."));
+ virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path",
mem_path, NULL);
+ rv = 0;
+ }
VIR_FREE(mem_path);
- return 0;
+ return rv;
}
static int
qemuBuildMemCommandLine(virCommandPtr cmd,
virQEMUDriverConfigPtr cfg,
- const virDomainDef *def,
- virQEMUCapsPtr qemuCaps)
+ const virDomainDefPtr def,
+ virQEMUCapsPtr qemuCaps,
+ virBitmapPtr auto_nodeset)
{
if (qemuDomainDefValidateMemoryHotplug(def, qemuCaps, NULL) < 0)
return -1;
@@ -7194,7 +7229,7 @@ qemuBuildMemCommandLine(virCommandPtr cmd,
* there is no numa node specified.
*/
if (!virDomainNumaGetNodeCount(def->numa) &&
- qemuBuildMemPathStr(cfg, def, qemuCaps, cmd) < 0)
+ qemuBuildMemPathStr(cfg, def, qemuCaps, cmd, auto_nodeset) < 0)
return -1;
if (def->mem.locked && !virQEMUCapsGet(qemuCaps,
QEMU_CAPS_REALTIME_MLOCK)) {
@@ -7331,7 +7366,7 @@ qemuBuildNumaArgStr(virQEMUDriverConfigPtr cfg,
}
if (!needBackend &&
- qemuBuildMemPathStr(cfg, def, qemuCaps, cmd) < 0)
+ qemuBuildMemPathStr(cfg, def, qemuCaps, cmd, auto_nodeset) < 0)
goto cleanup;
for (i = 0; i < ncells; i++) {
@@ -9381,7 +9416,7 @@ qemuBuildCommandLine(virQEMUDriverPtr driver,
if (!migrateURI && !snapshot && qemuDomainAlignMemorySizes(def) <
0)
goto error;
- if (qemuBuildMemCommandLine(cmd, cfg, def, qemuCaps) < 0)
+ if (qemuBuildMemCommandLine(cmd, cfg, def, qemuCaps, nodeset) < 0)
goto error;
if (qemuBuildSmpCommandLine(cmd, def) < 0)
diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h
index 2f2a6ff..1e97d76 100644
--- a/src/qemu/qemu_command.h
+++ b/src/qemu/qemu_command.h
@@ -126,7 +126,7 @@ int qemuBuildMemoryBackendStr(unsigned long long size,
int guestNode,
virBitmapPtr userNodeset,
virBitmapPtr autoNodeset,
- virDomainDefPtr def,
+ const virDomainDefPtr def,
virQEMUCapsPtr qemuCaps,
virQEMUDriverConfigPtr cfg,
const char **backendType,
--
2.10.0.297.gf6727b0
2:48 a.m.
On Wed, Oct 12, 2016 at 15:04:53 +1100, Sam Bobroff wrote:
At the moment, guests that are backed by hugepages in the host are
only able to use policy to control the placement of those hugepages
on a per-(guest-)CPU basis. Policy applied globally is ignored.
Such guests would use <memoryBacking><hugepages/></memoryBacking> and
a <numatune> block with <memory mode=... nodeset=.../> but no <memnode
.../> elements.
This patch corrects this by, in this specific case, changing the QEMU
command line from "-mem-prealloc -mem-path=..." (which cannot
specify NUMA policy) to "-object memory-backend-file ..." (which can).
Note: This is not visible to the guest and does not appear to create
a migration incompatibility.
Signed-off-by: Sam Bobroff <sam.bobroff(a)au1.ibm.com>
---
There was some discussion leading up to this patch, here:
https://www.redhat.com/archives/libvir-list/2016-October/msg00033.html
During that discussion it seemed that fixing this issue would cause
migration incompatibility but after some careful testing, it appears
that it only does when a memory-backend object is attached to a guest
NUMA node and that is not the case here. If only one is created, and
used globally (not attached via mem=<id>), the migration data does not
seem to be changed and so it seems reasonable to try something like
this patch.
This patch does work for my test cases but I don't claim a deep
understanding of the libvirt code so this is at least partly a RFC.
Comments welcome :-)
Cheers,
Sam.
src/qemu/qemu_command.c | 55 ++++++++++++++++++++++++++++++++++++++++---------
src/qemu/qemu_command.h | 2 +-
2 files changed, 46 insertions(+), 11 deletions(-)
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 0804133..c28c8f2 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3143,7 +3143,7 @@ qemuBuildMemoryBackendStr(unsigned long long size,
int guestNode,
virBitmapPtr userNodeset,
virBitmapPtr autoNodeset,
- virDomainDefPtr def,
+ const virDomainDefPtr def,
This does not work as expected. Using 'const' with types that hide the
pointer makes the pointer const and not the structure that the pointer
points to.
virQEMUCapsPtr qemuCaps,
virQEMUDriverConfigPtr cfg,
const char **backendType,
@@ -7129,12 +7129,18 @@ qemuBuildSmpCommandLine(virCommandPtr cmd,
static int
qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
- const virDomainDef *def,
+ const virDomainDefPtr def,
Same as above. This change is wrong.
virQEMUCapsPtr qemuCaps,
- virCommandPtr cmd)
+ virCommandPtr cmd,
+ virBitmapPtr auto_nodeset)
{
const long system_page_size = virGetSystemPageSizeKB();
char *mem_path = NULL;
+ virBitmapPtr nodemask = NULL;
+ const char *backendType = NULL;
+ char *backendStr = NULL;
+ virJSONValuePtr props;
+ int rv = -1;
/*
* No-op if hugepages were not requested.
@@ -7159,18 +7165,47 @@ qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
if (qemuGetHupageMemPath(cfg, def->mem.hugepages[0].size, &mem_path) < 0)
return -1;
- virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path",
mem_path, NULL);
+ if (virDomainNumatuneMaybeGetNodeset(def->numa, auto_nodeset,
+ &nodemask, -1) < 0)
+ return -1;
+ if (nodemask && virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE)) {
+ props = virJSONValueNewObject();
This is leaked, qemuBuildMemoryBackendStr allocates one itself.
+ if
(qemuBuildMemoryBackendStr(virDomainDefGetMemoryInitial(def),
+ 0, -1, NULL, auto_nodeset,
+ def, qemuCaps, cfg, &backendType,
+ &props, false) < 0)
+ goto cleanup;
+ if (!(backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType,
+ "mem",
+ props)))
+ goto cleanup;
So you create a memory object that does not get used ...
+ virCommandAddArgList(cmd, "-object", backendStr,
NULL);
So does qemu use memory objects that are not used magically as it's
memory? That seems odd. Could you please elaborate on this part and how
it's supposed to work? Without a proper elaboration how this is supposed
to work with qemu this patch is not acceptable.
+ rv = 0;
+cleanup:
This won't pass syntax check. Labels have to be spaced out.
+ VIR_FREE(backendStr);
+ VIR_FREE(props);
This is a JSON value object, you need to free it with the proper
function.
+ }
+ else {
This breaks coding style.
+ if (nodemask || 1)
Erm, a tautology?
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
"%s",
+ _("Memory file backend objects are "
+ "unsupported by QEMU binary. Global NUMA "
+ "hugepage policy will be ignored."));
Reporting an error but not terminating the startup is not acceptable.
Errors should not be reported unless something fails.
+ virCommandAddArgList(cmd, "-mem-prealloc",
"-mem-path", mem_path, NULL);
+ rv = 0;
+ }
VIR_FREE(mem_path);
- return 0;
+ return rv;
}
Missing a change to the test files. Please make sure that you run 'make
check' and 'make syntax-check' and send only patches that pass those.
Peter
7:57 p.m.
On Wed, Oct 12, 2016 at 09:48:07AM +0200, Peter Krempa wrote:
On Wed, Oct 12, 2016 at 15:04:53 +1100, Sam Bobroff wrote:
> At the moment, guests that are backed by hugepages in the host are
> only able to use policy to control the placement of those hugepages
> on a per-(guest-)CPU basis. Policy applied globally is ignored.
>
> Such guests would use <memoryBacking><hugepages/></memoryBacking>
and
> a <numatune> block with <memory mode=... nodeset=.../> but no
<memnode
> .../> elements.
>
> This patch corrects this by, in this specific case, changing the QEMU
> command line from "-mem-prealloc -mem-path=..." (which cannot
> specify NUMA policy) to "-object memory-backend-file ..." (which can).
>
> Note: This is not visible to the guest and does not appear to create
> a migration incompatibility.
>
> Signed-off-by: Sam Bobroff <sam.bobroff(a)au1.ibm.com>
> ---
> There was some discussion leading up to this patch, here:
>
> https://www.redhat.com/archives/libvir-list/2016-October/msg00033.html
>
> During that discussion it seemed that fixing this issue would cause
> migration incompatibility but after some careful testing, it appears
> that it only does when a memory-backend object is attached to a guest
> NUMA node and that is not the case here. If only one is created, and
> used globally (not attached via mem=<id>), the migration data does not
> seem to be changed and so it seems reasonable to try something like
> this patch.
>
> This patch does work for my test cases but I don't claim a deep
> understanding of the libvirt code so this is at least partly a RFC.
> Comments welcome :-)
>
> Cheers,
> Sam.
>
> src/qemu/qemu_command.c | 55 ++++++++++++++++++++++++++++++++++++++++---------
> src/qemu/qemu_command.h | 2 +-
> 2 files changed, 46 insertions(+), 11 deletions(-)
>
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 0804133..c28c8f2 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -3143,7 +3143,7 @@ qemuBuildMemoryBackendStr(unsigned long long size,
> int guestNode,
> virBitmapPtr userNodeset,
> virBitmapPtr autoNodeset,
> - virDomainDefPtr def,
> + const virDomainDefPtr def,
This does not work as expected. Using 'const' with types that hide the
pointer makes the pointer const and not the structure that the pointer
points to.
Ah, of course you're right.
> virQEMUCapsPtr qemuCaps,
> virQEMUDriverConfigPtr cfg,
> const char **backendType,
> @@ -7129,12 +7129,18 @@ qemuBuildSmpCommandLine(virCommandPtr cmd,
>
> static int
> qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
> - const virDomainDef *def,
> + const virDomainDefPtr def,
Same as above. This change is wrong.
OK.
> virQEMUCapsPtr qemuCaps,
> - virCommandPtr cmd)
> + virCommandPtr cmd,
> + virBitmapPtr auto_nodeset)
> {
> const long system_page_size = virGetSystemPageSizeKB();
> char *mem_path = NULL;
> + virBitmapPtr nodemask = NULL;
> + const char *backendType = NULL;
> + char *backendStr = NULL;
> + virJSONValuePtr props;
> + int rv = -1;
>
> /*
> * No-op if hugepages were not requested.
> @@ -7159,18 +7165,47 @@ qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
> if (qemuGetHupageMemPath(cfg, def->mem.hugepages[0].size, &mem_path)
< 0)
> return -1;
>
> - virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path",
mem_path, NULL);
> + if (virDomainNumatuneMaybeGetNodeset(def->numa, auto_nodeset,
> + &nodemask, -1) < 0)
> + return -1;
> + if (nodemask && virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE))
{
> + props = virJSONValueNewObject();
This is leaked, qemuBuildMemoryBackendStr allocates one itself.
Ah of course, sorry. I think I can just remove that line.
> + if
(qemuBuildMemoryBackendStr(virDomainDefGetMemoryInitial(def),
> + 0, -1, NULL, auto_nodeset,
> + def, qemuCaps, cfg, &backendType,
> + &props, false) < 0)
> + goto cleanup;
> + if (!(backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType,
> + "mem",
> + props)))
> + goto cleanup;
So you create a memory object that does not get used ...
Yes, that is correct.
> + virCommandAddArgList(cmd, "-object",
backendStr, NULL);
So does qemu use memory objects that are not used magically as it's
memory? That seems odd. Could you please elaborate on this part and how
it's supposed to work? Without a proper elaboration how this is supposed
to work with qemu this patch is not acceptable.
Yes, it did seem odd to me, but I didn't know if it was odd to anyone else! ;-)
I'll elaborate properly in the commit message if I end up doing a version 2
(and if the fix ends up using that method). But briefly, QEMU seems to treat a
single memory backend object, that is not linked to any NUMA node, just as it
would "-mem-path" and "-mem-prealloc" except that NUMA policy can also
be set.
It seems to "know" about this useage because it is careful to avoid changing
the "memory region" name to the ID in this case and it's that quirk that
allows migrations to be unaffected.
> + rv = 0;
> +cleanup:
This won't pass syntax check. Labels have to be spaced out.
Thanks, I'll use syntax check as noted below!
> + VIR_FREE(backendStr);
> + VIR_FREE(props);
This is a JSON value object, you need to free it with the proper
function.
Ah, virJSONValueFree(). Thanks.
> + }
> + else {
This breaks coding style.
OK.
> + if (nodemask || 1)
Erm, a tautology?
Yes, an embarassing bit of debug from the last round of testing :-P
(Testing the warning.)
> + virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
"%s",
> + _("Memory file backend objects are "
> + "unsupported by QEMU binary. Global NUMA "
> + "hugepage policy will be ignored."));
Reporting an error but not terminating the startup is not acceptable.
Errors should not be reported unless something fails.
Right, if I do another version I'll change this to a warning.
> + virCommandAddArgList(cmd, "-mem-prealloc",
"-mem-path", mem_path, NULL);
> + rv = 0;
> + }
> VIR_FREE(mem_path);
>
> - return 0;
> + return rv;
> }
>
Missing a change to the test files. Please make sure that you run 'make
check' and 'make syntax-check' and send only patches that pass those.
Ah, thanks. I will always use them in future.
Peter
Thanks for your revew!
Cheers,
Sam.
3:27 a.m.
On Wed, Oct 12, 2016 at 03:04:53PM +1100, Sam Bobroff wrote:
At the moment, guests that are backed by hugepages in the host are
only able to use policy to control the placement of those hugepages
on a per-(guest-)CPU basis. Policy applied globally is ignored.
Such guests would use <memoryBacking><hugepages/></memoryBacking> and
a <numatune> block with <memory mode=... nodeset=.../> but no <memnode
.../> elements.
This patch corrects this by, in this specific case, changing the QEMU
command line from "-mem-prealloc -mem-path=..." (which cannot
specify NUMA policy) to "-object memory-backend-file ..." (which can).
Note: This is not visible to the guest and does not appear to create
a migration incompatibility.
It could make sense, I haven't tried yet, though. However, I still
don't see the point in using memory-backend-file. Is it that when you
don't have cpuset cgroup the allocation doesn't work well? Because it
certainly does work for me.
Signed-off-by: Sam Bobroff <sam.bobroff(a)au1.ibm.com>
---
There was some discussion leading up to this patch, here:
https://www.redhat.com/archives/libvir-list/2016-October/msg00033.html
During that discussion it seemed that fixing this issue would cause
migration incompatibility but after some careful testing, it appears
that it only does when a memory-backend object is attached to a guest
NUMA node and that is not the case here. If only one is created, and
used globally (not attached via mem=<id>), the migration data does not
seem to be changed and so it seems reasonable to try something like
this patch.
This patch does work for my test cases but I don't claim a deep
understanding of the libvirt code so this is at least partly a RFC.
Comments welcome :-)
Cheers,
Sam.
src/qemu/qemu_command.c | 55 ++++++++++++++++++++++++++++++++++++++++---------
src/qemu/qemu_command.h | 2 +-
2 files changed, 46 insertions(+), 11 deletions(-)
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 0804133..c28c8f2 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3143,7 +3143,7 @@ qemuBuildMemoryBackendStr(unsigned long long size,
int guestNode,
virBitmapPtr userNodeset,
virBitmapPtr autoNodeset,
- virDomainDefPtr def,
+ const virDomainDefPtr def,
virQEMUCapsPtr qemuCaps,
virQEMUDriverConfigPtr cfg,
const char **backendType,
@@ -7129,12 +7129,18 @@ qemuBuildSmpCommandLine(virCommandPtr cmd,
static int
qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
- const virDomainDef *def,
+ const virDomainDefPtr def,
These two hunks have nothing to do with the change. If you want to do
them for some reason, explain the reasoning and put it into separate
patch, please.
virQEMUCapsPtr qemuCaps,
- virCommandPtr cmd)
+ virCommandPtr cmd,
+ virBitmapPtr auto_nodeset)
{
const long system_page_size = virGetSystemPageSizeKB();
char *mem_path = NULL;
+ virBitmapPtr nodemask = NULL;
+ const char *backendType = NULL;
+ char *backendStr = NULL;
+ virJSONValuePtr props;
+ int rv = -1;
/*
* No-op if hugepages were not requested.
@@ -7159,18 +7165,47 @@ qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
if (qemuGetHupageMemPath(cfg, def->mem.hugepages[0].size, &mem_path) < 0)
return -1;
- virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path", mem_path,
NULL);
+ if (virDomainNumatuneMaybeGetNodeset(def->numa, auto_nodeset,
+ &nodemask, -1) < 0)
+ return -1;
+ if (nodemask && virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE)) {
+ props = virJSONValueNewObject();
+ if (qemuBuildMemoryBackendStr(virDomainDefGetMemoryInitial(def),
+ 0, -1, NULL, auto_nodeset,
+ def, qemuCaps, cfg, &backendType,
+ &props, false) < 0)
+ goto cleanup;
+ if (!(backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType,
+ "mem",
+ props)))
+ goto cleanup;
+ virCommandAddArgList(cmd, "-object", backendStr, NULL);
So now a function that's called BuildMemPathStr does more than that. It
is also called when the memory is added in a different way in which case
this function would just add even more memory which is clearly wrong.
+ rv = 0;
+cleanup:
+ VIR_FREE(backendStr);
+ VIR_FREE(props);
+ }
+ else {
+ if (nodemask || 1)
" || 1" ? Leftover from debugging?
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
"%s",
+ _("Memory file backend objects are "
+ "unsupported by QEMU binary. Global NUMA "
+ "hugepage policy will be ignored."));
Reporting error without erroring out is wrong. VIR_WARN is probably
what you wanted to do here.
As I said, I don't feel the need for the change. If there is a need for
it, it should clearly be done differently, so NACK to this particular
patch.
Martin
7:34 p.m.
On Wed, Oct 12, 2016 at 10:27:50AM +0200, Martin Kletzander wrote:
On Wed, Oct 12, 2016 at 03:04:53PM +1100, Sam Bobroff wrote:
>At the moment, guests that are backed by hugepages in the host are
>only able to use policy to control the placement of those hugepages
>on a per-(guest-)CPU basis. Policy applied globally is ignored.
>
>Such guests would use <memoryBacking><hugepages/></memoryBacking>
and
>a <numatune> block with <memory mode=... nodeset=.../> but no
<memnode
>.../> elements.
>
>This patch corrects this by, in this specific case, changing the QEMU
>command line from "-mem-prealloc -mem-path=..." (which cannot
>specify NUMA policy) to "-object memory-backend-file ..." (which can).
>
>Note: This is not visible to the guest and does not appear to create
>a migration incompatibility.
>
It could make sense, I haven't tried yet, though. However, I still
don't see the point in using memory-backend-file. Is it that when you
don't have cpuset cgroup the allocation doesn't work well? Because it
certainly does work for me.
Thanks for taking a look at this :-)
The point of using a memory-backend-file is that with it, the NUMA policy can
be specified to QEMU, but with -mem-path it can't. It seems to be a way to tell
QEMU to apply NUMA policy in the right place. It does seem odd to me to use
memory-backend-file without attaching the backend to a guest NUMA node, but it
seems to do the right thing in this case. (If there are guest NUMA nodes, or if
hugepages aren't being used, policy is correctly applied.)
I'll describe my test case in detail, perhaps there's something I don't
understand
happening.
* I set up a machine with two (fake) NUMA nodes (0 and 1), with 2G of hugepages
on node 1, and none on node 0.
* I create a 2G guest using virt-install:
virt-install --name ppc --memory=2048 --disk ~/tmp/tmp.qcow2 --cdrom
~/tmp/ubuntu-16.04-server-ppc64el.iso --wait 0 --virt-type qemu --memorybacking
hugepages=on --graphics vnc --arch ppc64le
* I "virsh destroy" and then "virsh edit" to add this block to the
guest XML:
<numatune>
<memory mode='strict' nodeset='0'/>
</numatune>
* "virsh start", and the machine starts (I believe it should fail due to
insufficient memory satasfying the policy).
* "numastat -p $(pidof qemu-system-ppc64)" shows something like this:
Per-node process memory usage (in MBs) for PID 8048 (qemu-system-ppc)
Node 0 Node 1 Total
--------------- --------------- ---------------
Huge 0.00 2048.00 2048.00
Heap 8.12 0.00 8.12
Stack 0.03 0.00 0.03
Private 35.80 6.10 41.90
---------------- --------------- --------------- ---------------
Total 43.95 2054.10 2098.05
So it looks like it's allocated hugepages from node 1, isn't this violating the
policy I set via numatune?
>Signed-off-by: Sam Bobroff <sam.bobroff(a)au1.ibm.com>
>---
>There was some discussion leading up to this patch, here:
>
>https://www.redhat.com/archives/libvir-list/2016-October/msg00033.html
>
>During that discussion it seemed that fixing this issue would cause
>migration incompatibility but after some careful testing, it appears
>that it only does when a memory-backend object is attached to a guest
>NUMA node and that is not the case here. If only one is created, and
>used globally (not attached via mem=<id>), the migration data does not
>seem to be changed and so it seems reasonable to try something like
>this patch.
>
>This patch does work for my test cases but I don't claim a deep
>understanding of the libvirt code so this is at least partly a RFC.
>Comments welcome :-)
>
>Cheers,
>Sam.
>
>src/qemu/qemu_command.c | 55 ++++++++++++++++++++++++++++++++++++++++---------
>src/qemu/qemu_command.h | 2 +-
>2 files changed, 46 insertions(+), 11 deletions(-)
>
>diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
>index 0804133..c28c8f2 100644
>--- a/src/qemu/qemu_command.c
>+++ b/src/qemu/qemu_command.c
>@@ -3143,7 +3143,7 @@ qemuBuildMemoryBackendStr(unsigned long long size,
> int guestNode,
> virBitmapPtr userNodeset,
> virBitmapPtr autoNodeset,
>- virDomainDefPtr def,
>+ const virDomainDefPtr def,
> virQEMUCapsPtr qemuCaps,
> virQEMUDriverConfigPtr cfg,
> const char **backendType,
>@@ -7129,12 +7129,18 @@ qemuBuildSmpCommandLine(virCommandPtr cmd,
>
>static int
>qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
>- const virDomainDef *def,
>+ const virDomainDefPtr def,
These two hunks have nothing to do with the change. If you want to do
them for some reason, explain the reasoning and put it into separate
patch, please.
OK.
> virQEMUCapsPtr qemuCaps,
>- virCommandPtr cmd)
>+ virCommandPtr cmd,
>+ virBitmapPtr auto_nodeset)
>{
> const long system_page_size = virGetSystemPageSizeKB();
> char *mem_path = NULL;
>+ virBitmapPtr nodemask = NULL;
>+ const char *backendType = NULL;
>+ char *backendStr = NULL;
>+ virJSONValuePtr props;
>+ int rv = -1;
>
> /*
> * No-op if hugepages were not requested.
>@@ -7159,18 +7165,47 @@ qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg,
> if (qemuGetHupageMemPath(cfg, def->mem.hugepages[0].size, &mem_path) <
0)
> return -1;
>
>- virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path",
mem_path, NULL);
>+ if (virDomainNumatuneMaybeGetNodeset(def->numa, auto_nodeset,
>+ &nodemask, -1) < 0)
>+ return -1;
>+ if (nodemask && virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE))
{
>+ props = virJSONValueNewObject();
>+ if (qemuBuildMemoryBackendStr(virDomainDefGetMemoryInitial(def),
>+ 0, -1, NULL, auto_nodeset,
>+ def, qemuCaps, cfg, &backendType,
>+ &props, false) < 0)
>+ goto cleanup;
>+ if (!(backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType,
>+ "mem",
>+ props)))
>+ goto cleanup;
>+ virCommandAddArgList(cmd, "-object", backendStr, NULL);
So now a function that's called BuildMemPathStr does more than that. It
is also called when the memory is added in a different way in which case
this function would just add even more memory which is clearly wrong.
I'm not sure if I understand this; this function used to add "-mem-path"
and it would now add either "-mem-path" or a memory backend (with the same
path), both doing the same kind of configuration (is that not the case?). I did
see that it must not be called twice (which was already the case, I think), but
I convinced myself that it would only be called once: There are only two
callers of qemuBuildMemPathStr(). One is in qemuBuildMemCommandLine() and it is
protected by "if (!virDomainNumaGetNodeCount(def->numa)", and the other is
in
qemuBuildNumaArgStr() and the (only) call to that is protected by "if
(virDomainNumaGetNodeCount(def->numa)". Is that safe enough?
>+ rv = 0;
>+cleanup:
>+ VIR_FREE(backendStr);
>+ VIR_FREE(props);
>+ }
>+ else {
>+ if (nodemask || 1)
" || 1" ? Leftover from debugging?
Oops, yes.
>+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
"%s",
>+ _("Memory file backend objects are "
>+ "unsupported by QEMU binary. Global NUMA "
>+ "hugepage policy will be ignored."));
Reporting error without erroring out is wrong. VIR_WARN is probably
what you wanted to do here.
OK.
As I said, I don't feel the need for the change. If there is a
need for
it, it should clearly be done differently, so NACK to this particular
patch.
Martin
I understand. I'm interested to see what you think of the test case :-)
Cheers,
Sam.
4:34 a.m.
On Thu, Oct 13, 2016 at 11:34:16AM +1100, Sam Bobroff wrote:
On Wed, Oct 12, 2016 at 10:27:50AM +0200, Martin Kletzander wrote:
> On Wed, Oct 12, 2016 at 03:04:53PM +1100, Sam Bobroff wrote:
> >At the moment, guests that are backed by hugepages in the host are
> >only able to use policy to control the placement of those hugepages
> >on a per-(guest-)CPU basis. Policy applied globally is ignored.
> >
> >Such guests would use
<memoryBacking><hugepages/></memoryBacking> and
> >a <numatune> block with <memory mode=... nodeset=.../> but no
<memnode
> >.../> elements.
> >
> >This patch corrects this by, in this specific case, changing the QEMU
> >command line from "-mem-prealloc -mem-path=..." (which cannot
> >specify NUMA policy) to "-object memory-backend-file ..." (which can).
> >
> >Note: This is not visible to the guest and does not appear to create
> >a migration incompatibility.
> >
>
> It could make sense, I haven't tried yet, though. However, I still
> don't see the point in using memory-backend-file. Is it that when you
> don't have cpuset cgroup the allocation doesn't work well? Because it
> certainly does work for me.
Thanks for taking a look at this :-)
The point of using a memory-backend-file is that with it, the NUMA policy can
be specified to QEMU, but with -mem-path it can't. It seems to be a way to tell
QEMU to apply NUMA policy in the right place. It does seem odd to me to use
memory-backend-file without attaching the backend to a guest NUMA node, but it
seems to do the right thing in this case. (If there are guest NUMA nodes, or if
hugepages aren't being used, policy is correctly applied.)
I'll describe my test case in detail, perhaps there's something I don't
understand
happening.
* I set up a machine with two (fake) NUMA nodes (0 and 1), with 2G of hugepages
on node 1, and none on node 0.
* I create a 2G guest using virt-install:
virt-install --name ppc --memory=2048 --disk ~/tmp/tmp.qcow2 --cdrom
~/tmp/ubuntu-16.04-server-ppc64el.iso --wait 0 --virt-type qemu --memorybacking
hugepages=on --graphics vnc --arch ppc64le
* I "virsh destroy" and then "virsh edit" to add this block to the
guest XML:
<numatune>
<memory mode='strict' nodeset='0'/>
</numatune>
* "virsh start", and the machine starts (I believe it should fail due to
insufficient memory satasfying the policy).
* "numastat -p $(pidof qemu-system-ppc64)" shows something like this:
Per-node process memory usage (in MBs) for PID 8048 (qemu-system-ppc)
Node 0 Node 1 Total
--------------- --------------- ---------------
Huge 0.00 2048.00 2048.00
Heap 8.12 0.00 8.12
Stack 0.03 0.00 0.03
Private 35.80 6.10 41.90
---------------- --------------- --------------- ---------------
Total 43.95 2054.10 2098.05
So it looks like it's allocated hugepages from node 1, isn't this violating the
policy I set via numatune?
Oh, now I get it. We are doing our best to apply that policy to qemu
even when we don't have this option. However, using this works even
better (which is probably* what we want). And that's the reasoning
behind this.
* I'm saying probably because when I was adding numactl binding to be
used together with cgroups, I was told that we couldn't change the
binding afterwards and it's bad. I feel like we could do something
with that and it would help us in the future, but there needs to be a
discussion, I guess. Because I might be one of the few =)
So to recapitulate that, there are three options how to affect the
allocation of qemu's memory:
1) numactl (libnuma): it works as expected, but cannot be changed later
2) cgroups: so strict it has to be applied after qemu started, due to
that it doesn't work right, especially for stuff that gets all
pre-allocated (like hugepages). it can be changed later, but it
won't always mean the memory will migrate, so upon change there is
no guarantee. If it's unavailable, we fallback to (1) anyway
3) memory-backing-file's host-nodes=: this works as expected, but
cannot be used with older QEMUs, cannot be changed later and in some
cases (not your particular one) it might screw up migration if it
wasn't used before.
Selecting the best option from these, plus making the code work with
every possibility (erroring out when you want to change the memory node
and we had to use (1) for example) is a pain. We should really think
about that and reorganize these things for the better of the future.
Otherwise we're going to get overwhelm ourselves. Cc'ing Peter to get
his thoughts as well as he worked on some parts of this as well.
Martin
7:52 p.m.
On Thu, Oct 13, 2016 at 11:34:43AM +0200, Martin Kletzander wrote:
On Thu, Oct 13, 2016 at 11:34:16AM +1100, Sam Bobroff wrote:
>On Wed, Oct 12, 2016 at 10:27:50AM +0200, Martin Kletzander wrote:
>>On Wed, Oct 12, 2016 at 03:04:53PM +1100, Sam Bobroff wrote:
>>>At the moment, guests that are backed by hugepages in the host are
>>>only able to use policy to control the placement of those hugepages
>>>on a per-(guest-)CPU basis. Policy applied globally is ignored.
>>>
>>>Such guests would use
<memoryBacking><hugepages/></memoryBacking> and
>>>a <numatune> block with <memory mode=... nodeset=.../> but no
<memnode
>>>.../> elements.
>>>
>>>This patch corrects this by, in this specific case, changing the QEMU
>>>command line from "-mem-prealloc -mem-path=..." (which cannot
>>>specify NUMA policy) to "-object memory-backend-file ..." (which
can).
>>>
>>>Note: This is not visible to the guest and does not appear to create
>>>a migration incompatibility.
>>>
>>
>>It could make sense, I haven't tried yet, though. However, I still
>>don't see the point in using memory-backend-file. Is it that when you
>>don't have cpuset cgroup the allocation doesn't work well? Because it
>>certainly does work for me.
>
>Thanks for taking a look at this :-)
>
>The point of using a memory-backend-file is that with it, the NUMA policy can
>be specified to QEMU, but with -mem-path it can't. It seems to be a way to tell
>QEMU to apply NUMA policy in the right place. It does seem odd to me to use
>memory-backend-file without attaching the backend to a guest NUMA node, but it
>seems to do the right thing in this case. (If there are guest NUMA nodes, or if
>hugepages aren't being used, policy is correctly applied.)
>
>I'll describe my test case in detail, perhaps there's something I don't
understand
>happening.
>
>* I set up a machine with two (fake) NUMA nodes (0 and 1), with 2G of hugepages
> on node 1, and none on node 0.
>
>* I create a 2G guest using virt-install:
>
>virt-install --name ppc --memory=2048 --disk ~/tmp/tmp.qcow2 --cdrom
~/tmp/ubuntu-16.04-server-ppc64el.iso --wait 0 --virt-type qemu --memorybacking
hugepages=on --graphics vnc --arch ppc64le
>
>* I "virsh destroy" and then "virsh edit" to add this block to
the guest XML:
>
> <numatune>
> <memory mode='strict' nodeset='0'/>
> </numatune>
>
>* "virsh start", and the machine starts (I believe it should fail due to
insufficient memory satasfying the policy).
>* "numastat -p $(pidof qemu-system-ppc64)" shows something like this:
>
>Per-node process memory usage (in MBs) for PID 8048 (qemu-system-ppc)
> Node 0 Node 1 Total
> --------------- --------------- ---------------
>Huge 0.00 2048.00 2048.00
>Heap 8.12 0.00 8.12
>Stack 0.03 0.00 0.03
>Private 35.80 6.10 41.90
>---------------- --------------- --------------- ---------------
>Total 43.95 2054.10 2098.05
>
>So it looks like it's allocated hugepages from node 1, isn't this violating
the
>policy I set via numatune?
>
Oh, now I get it. We are doing our best to apply that policy to qemu
even when we don't have this option. However, using this works even
better (which is probably* what we want). And that's the reasoning
behind this.
* I'm saying probably because when I was adding numactl binding to be
used together with cgroups, I was told that we couldn't change the
binding afterwards and it's bad. I feel like we could do something
with that and it would help us in the future, but there needs to be a
discussion, I guess. Because I might be one of the few =)
So to recapitulate that, there are three options how to affect the
allocation of qemu's memory:
1) numactl (libnuma): it works as expected, but cannot be changed later
2) cgroups: so strict it has to be applied after qemu started, due to
that it doesn't work right, especially for stuff that gets all
pre-allocated (like hugepages). it can be changed later, but it
won't always mean the memory will migrate, so upon change there is
no guarantee. If it's unavailable, we fallback to (1) anyway
3) memory-backing-file's host-nodes=: this works as expected, but
cannot be used with older QEMUs, cannot be changed later and in some
cases (not your particular one) it might screw up migration if it
wasn't used before.
Selecting the best option from these, plus making the code work with
every possibility (erroring out when you want to change the memory node
and we had to use (1) for example) is a pain. We should really think
about that and reorganize these things for the better of the future.
Otherwise we're going to get overwhelm ourselves. Cc'ing Peter to get
his thoughts as well as he worked on some parts of this as well.
Martin
Thanks for the explanation, and I agree (I'm already a bit overwhelmed!) :-)
What do you mean by "changed later"? Do you mean, if the domain XML is changed
while the machine is running?
I did look at the libnuma and cgroups approaches, but I was concerned they
wouldn't work in this case, because of the way QEMU allocates memory when
mem-prealloc is used: the memory is allocated in the main process, before the
CPU threads are created. (This is based only on a bit of hacking and debugging
in QEMU, but it does seem explain the behaviour I've seen so far.)
If this is the case, it would seem to be a significant problem: if policy is
set on the main thread, it will affect all allocations not just the VCPU
memory and if it's set on the VCPU threads it won't catch the pre-allocation at
all. (Is this what you were referring to by "it doesn't work right"?)
That was my reasoning for trying to use the backend object in this case; it was
the only method that worked and did not require changes to QEMU. I'd prefer
the other approaches if they could be made to work.
I think QEMU could be altered to move the preallocations into the VCPU
threads but it didn't seem trivial and I suspected the QEMU community would
point out that there was already a way to do it using backend objects. Another
option would be to add a -host-nodes parameter to QEMU so that the policy can
be given without adding a memory backend object. (That seems like a more
reasonable change to QEMU.)
Cheers,
Sam.
3:19 a.m.
On Fri, Oct 14, 2016 at 11:52:22AM +1100, Sam Bobroff wrote:
On Thu, Oct 13, 2016 at 11:34:43AM +0200, Martin Kletzander wrote:
> On Thu, Oct 13, 2016 at 11:34:16AM +1100, Sam Bobroff wrote:
> >On Wed, Oct 12, 2016 at 10:27:50AM +0200, Martin Kletzander wrote:
> >>On Wed, Oct 12, 2016 at 03:04:53PM +1100, Sam Bobroff wrote:
> >>>At the moment, guests that are backed by hugepages in the host are
> >>>only able to use policy to control the placement of those hugepages
> >>>on a per-(guest-)CPU basis. Policy applied globally is ignored.
> >>>
> >>>Such guests would use
<memoryBacking><hugepages/></memoryBacking> and
> >>>a <numatune> block with <memory mode=... nodeset=.../> but no
<memnode
> >>>.../> elements.
> >>>
> >>>This patch corrects this by, in this specific case, changing the QEMU
> >>>command line from "-mem-prealloc -mem-path=..." (which cannot
> >>>specify NUMA policy) to "-object memory-backend-file ..."
(which can).
> >>>
> >>>Note: This is not visible to the guest and does not appear to create
> >>>a migration incompatibility.
> >>>
> >>
> >>It could make sense, I haven't tried yet, though. However, I still
> >>don't see the point in using memory-backend-file. Is it that when you
> >>don't have cpuset cgroup the allocation doesn't work well? Because
it
> >>certainly does work for me.
> >
> >Thanks for taking a look at this :-)
> >
> >The point of using a memory-backend-file is that with it, the NUMA policy can
> >be specified to QEMU, but with -mem-path it can't. It seems to be a way to
tell
> >QEMU to apply NUMA policy in the right place. It does seem odd to me to use
> >memory-backend-file without attaching the backend to a guest NUMA node, but it
> >seems to do the right thing in this case. (If there are guest NUMA nodes, or if
> >hugepages aren't being used, policy is correctly applied.)
> >
> >I'll describe my test case in detail, perhaps there's something I
don't understand
> >happening.
> >
> >* I set up a machine with two (fake) NUMA nodes (0 and 1), with 2G of hugepages
> > on node 1, and none on node 0.
> >
> >* I create a 2G guest using virt-install:
> >
> >virt-install --name ppc --memory=2048 --disk ~/tmp/tmp.qcow2 --cdrom
~/tmp/ubuntu-16.04-server-ppc64el.iso --wait 0 --virt-type qemu --memorybacking
hugepages=on --graphics vnc --arch ppc64le
> >
> >* I "virsh destroy" and then "virsh edit" to add this block
to the guest XML:
> >
> > <numatune>
> > <memory mode='strict' nodeset='0'/>
> > </numatune>
> >
> >* "virsh start", and the machine starts (I believe it should fail due
to insufficient memory satasfying the policy).
> >* "numastat -p $(pidof qemu-system-ppc64)" shows something like this:
> >
> >Per-node process memory usage (in MBs) for PID 8048 (qemu-system-ppc)
> > Node 0 Node 1 Total
> > --------------- --------------- ---------------
> >Huge 0.00 2048.00 2048.00
> >Heap 8.12 0.00 8.12
> >Stack 0.03 0.00 0.03
> >Private 35.80 6.10 41.90
> >---------------- --------------- --------------- ---------------
> >Total 43.95 2054.10 2098.05
> >
> >So it looks like it's allocated hugepages from node 1, isn't this
violating the
> >policy I set via numatune?
> >
>
> Oh, now I get it. We are doing our best to apply that policy to qemu
> even when we don't have this option. However, using this works even
> better (which is probably* what we want). And that's the reasoning
> behind this.
>
> * I'm saying probably because when I was adding numactl binding to be
> used together with cgroups, I was told that we couldn't change the
> binding afterwards and it's bad. I feel like we could do something
> with that and it would help us in the future, but there needs to be a
> discussion, I guess. Because I might be one of the few =)
>
> So to recapitulate that, there are three options how to affect the
> allocation of qemu's memory:
>
> 1) numactl (libnuma): it works as expected, but cannot be changed later
>
> 2) cgroups: so strict it has to be applied after qemu started, due to
> that it doesn't work right, especially for stuff that gets all
> pre-allocated (like hugepages). it can be changed later, but it
> won't always mean the memory will migrate, so upon change there is
> no guarantee. If it's unavailable, we fallback to (1) anyway
>
> 3) memory-backing-file's host-nodes=: this works as expected, but
> cannot be used with older QEMUs, cannot be changed later and in some
> cases (not your particular one) it might screw up migration if it
> wasn't used before.
>
> Selecting the best option from these, plus making the code work with
> every possibility (erroring out when you want to change the memory node
> and we had to use (1) for example) is a pain. We should really think
> about that and reorganize these things for the better of the future.
> Otherwise we're going to get overwhelm ourselves. Cc'ing Peter to get
> his thoughts as well as he worked on some parts of this as well.
>
> Martin
Thanks for the explanation, and I agree (I'm already a bit overwhelmed!) :-)
What do you mean by "changed later"? Do you mean, if the domain XML is changed
while the machine is running?
E.g. by 'virsh numatune domain 1-2'
I did look at the libnuma and cgroups approaches, but I was concerned
they
wouldn't work in this case, because of the way QEMU allocates memory when
mem-prealloc is used: the memory is allocated in the main process, before the
CPU threads are created. (This is based only on a bit of hacking and debugging
in QEMU, but it does seem explain the behaviour I've seen so far.)
But we use numactl before QEMU is exec()'d.
If this is the case, it would seem to be a significant problem: if
policy is
set on the main thread, it will affect all allocations not just the VCPU
memory and if it's set on the VCPU threads it won't catch the pre-allocation at
all. (Is this what you were referring to by "it doesn't work right"?)
Kind of, yes.
That was my reasoning for trying to use the backend object in this
case; it was
the only method that worked and did not require changes to QEMU. I'd prefer
the other approaches if they could be made to work.
There is a workaround, you can disable the cpuset cgroup in
libvirtd.conf, but that's not what you want, I guess.
I think QEMU could be altered to move the preallocations into the
VCPU
threads but it didn't seem trivial and I suspected the QEMU community would
point out that there was already a way to do it using backend objects. Another
option would be to add a -host-nodes parameter to QEMU so that the policy can
be given without adding a memory backend object. (That seems like a more
reasonable change to QEMU.)
I think upstream won't like that, mostly because there is already a
way. And that is using memory-backend object. I think we could just
use that and disable changing it live. But upstream will probably want
that to be configurable or something.
Cheers,
Sam.
11:45 p.m.
On Fri, Oct 14, 2016 at 10:19:42AM +0200, Martin Kletzander wrote:
On Fri, Oct 14, 2016 at 11:52:22AM +1100, Sam Bobroff wrote:
>On Thu, Oct 13, 2016 at 11:34:43AM +0200, Martin Kletzander wrote:
>>On Thu, Oct 13, 2016 at 11:34:16AM +1100, Sam Bobroff wrote:
>>>On Wed, Oct 12, 2016 at 10:27:50AM +0200, Martin Kletzander wrote:
>>>>On Wed, Oct 12, 2016 at 03:04:53PM +1100, Sam Bobroff wrote:
>>>>>At the moment, guests that are backed by hugepages in the host are
>>>>>only able to use policy to control the placement of those hugepages
>>>>>on a per-(guest-)CPU basis. Policy applied globally is ignored.
>>>>>
>>>>>Such guests would use
<memoryBacking><hugepages/></memoryBacking> and
>>>>>a <numatune> block with <memory mode=... nodeset=.../>
but no <memnode
>>>>>.../> elements.
>>>>>
>>>>>This patch corrects this by, in this specific case, changing the
QEMU
>>>>>command line from "-mem-prealloc -mem-path=..." (which
cannot
>>>>>specify NUMA policy) to "-object memory-backend-file ..."
(which can).
>>>>>
>>>>>Note: This is not visible to the guest and does not appear to create
>>>>>a migration incompatibility.
>>>>>
>>>>
>>>>It could make sense, I haven't tried yet, though. However, I still
>>>>don't see the point in using memory-backend-file. Is it that when
you
>>>>don't have cpuset cgroup the allocation doesn't work well?
Because it
>>>>certainly does work for me.
>>>
>>>Thanks for taking a look at this :-)
>>>
>>>The point of using a memory-backend-file is that with it, the NUMA policy
can
>>>be specified to QEMU, but with -mem-path it can't. It seems to be a way
to tell
>>>QEMU to apply NUMA policy in the right place. It does seem odd to me to use
>>>memory-backend-file without attaching the backend to a guest NUMA node, but
it
>>>seems to do the right thing in this case. (If there are guest NUMA nodes, or
if
>>>hugepages aren't being used, policy is correctly applied.)
>>>
>>>I'll describe my test case in detail, perhaps there's something I
don't understand
>>>happening.
>>>
>>>* I set up a machine with two (fake) NUMA nodes (0 and 1), with 2G of
hugepages
>>> on node 1, and none on node 0.
>>>
>>>* I create a 2G guest using virt-install:
>>>
>>>virt-install --name ppc --memory=2048 --disk ~/tmp/tmp.qcow2 --cdrom
~/tmp/ubuntu-16.04-server-ppc64el.iso --wait 0 --virt-type qemu --memorybacking
hugepages=on --graphics vnc --arch ppc64le
>>>
>>>* I "virsh destroy" and then "virsh edit" to add this
block to the guest XML:
>>>
>>> <numatune>
>>> <memory mode='strict' nodeset='0'/>
>>> </numatune>
>>>
>>>* "virsh start", and the machine starts (I believe it should fail
due to insufficient memory satasfying the policy).
>>>* "numastat -p $(pidof qemu-system-ppc64)" shows something like
this:
>>>
>>>Per-node process memory usage (in MBs) for PID 8048 (qemu-system-ppc)
>>> Node 0 Node 1 Total
>>> --------------- --------------- ---------------
>>>Huge 0.00 2048.00 2048.00
>>>Heap 8.12 0.00 8.12
>>>Stack 0.03 0.00 0.03
>>>Private 35.80 6.10 41.90
>>>---------------- --------------- --------------- ---------------
>>>Total 43.95 2054.10 2098.05
>>>
>>>So it looks like it's allocated hugepages from node 1, isn't this
violating the
>>>policy I set via numatune?
>>>
>>
>>Oh, now I get it. We are doing our best to apply that policy to qemu
>>even when we don't have this option. However, using this works even
>>better (which is probably* what we want). And that's the reasoning
>>behind this.
>>
>>* I'm saying probably because when I was adding numactl binding to be
>> used together with cgroups, I was told that we couldn't change the
>> binding afterwards and it's bad. I feel like we could do something
>> with that and it would help us in the future, but there needs to be a
>> discussion, I guess. Because I might be one of the few =)
>>
>>So to recapitulate that, there are three options how to affect the
>>allocation of qemu's memory:
>>
>>1) numactl (libnuma): it works as expected, but cannot be changed later
>>
>>2) cgroups: so strict it has to be applied after qemu started, due to
>> that it doesn't work right, especially for stuff that gets all
>> pre-allocated (like hugepages). it can be changed later, but it
>> won't always mean the memory will migrate, so upon change there is
>> no guarantee. If it's unavailable, we fallback to (1) anyway
>>
>>3) memory-backing-file's host-nodes=: this works as expected, but
>> cannot be used with older QEMUs, cannot be changed later and in some
>> cases (not your particular one) it might screw up migration if it
>> wasn't used before.
>>
>>Selecting the best option from these, plus making the code work with
>>every possibility (erroring out when you want to change the memory node
>>and we had to use (1) for example) is a pain. We should really think
>>about that and reorganize these things for the better of the future.
>>Otherwise we're going to get overwhelm ourselves. Cc'ing Peter to get
>>his thoughts as well as he worked on some parts of this as well.
>>
>>Martin
>
>Thanks for the explanation, and I agree (I'm already a bit overwhelmed!) :-)
>
>What do you mean by "changed later"? Do you mean, if the domain XML is
changed
>while the machine is running?
>
E.g. by 'virsh numatune domain 1-2'
Ah, thanks!
>I did look at the libnuma and cgroups approaches, but I was
concerned they
>wouldn't work in this case, because of the way QEMU allocates memory when
>mem-prealloc is used: the memory is allocated in the main process, before the
>CPU threads are created. (This is based only on a bit of hacking and debugging
>in QEMU, but it does seem explain the behaviour I've seen so far.)
>
But we use numactl before QEMU is exec()'d.
Sorry, I jumped ahead a bit. I'll try to explain what I mean:
I think the problem with using this method would be that the NUMA policy is
applied to all allocations by QEMU, not just ones related to the memory
backing. I'm not sure if that would cause a serious problem but it seems untidy,
and it doesn't happen in other situations (i.e. with separate memory backend
objects, QEMU sets up the policy specifically for each one and other
allocations aren't affected, AFAIK). Presumably, if memory were very
restricted it could prevent the guest from starting.
>If this is the case, it would seem to be a significant problem:
if policy is
>set on the main thread, it will affect all allocations not just the VCPU
>memory and if it's set on the VCPU threads it won't catch the pre-allocation
at
>all. (Is this what you were referring to by "it doesn't work right"?)
>
Kind of, yes.
>That was my reasoning for trying to use the backend object in this case; it was
>the only method that worked and did not require changes to QEMU. I'd prefer
>the other approaches if they could be made to work.
>
There is a workaround, you can disable the cpuset cgroup in
libvirtd.conf, but that's not what you want, I guess.
Thanks, but no it doesn't seem to be what I want due to the above issue.
>I think QEMU could be altered to move the preallocations into the
VCPU
>threads but it didn't seem trivial and I suspected the QEMU community would
>point out that there was already a way to do it using backend objects. Another
>option would be to add a -host-nodes parameter to QEMU so that the policy can
>be given without adding a memory backend object. (That seems like a more
>reasonable change to QEMU.)
>
I think upstream won't like that, mostly because there is already a
way. And that is using memory-backend object. I think we could just
use that and disable changing it live. But upstream will probably want
that to be configurable or something.
Right, but isn't this already an issue in the cases where libvirt is already
using memory backend objects and NUMA policy? (Or does libvirt already disable
changing it live in those situations?)
>Cheers,
>Sam.
>
3:43 p.m.
On Mon, Oct 17, 2016 at 03:45:09PM +1100, Sam Bobroff wrote:
On Fri, Oct 14, 2016 at 10:19:42AM +0200, Martin Kletzander wrote:
> On Fri, Oct 14, 2016 at 11:52:22AM +1100, Sam Bobroff wrote:
> >I did look at the libnuma and cgroups approaches, but I was concerned they
> >wouldn't work in this case, because of the way QEMU allocates memory when
> >mem-prealloc is used: the memory is allocated in the main process, before the
> >CPU threads are created. (This is based only on a bit of hacking and debugging
> >in QEMU, but it does seem explain the behaviour I've seen so far.)
> >
>
> But we use numactl before QEMU is exec()'d.
Sorry, I jumped ahead a bit. I'll try to explain what I mean:
I think the problem with using this method would be that the NUMA policy is
applied to all allocations by QEMU, not just ones related to the memory
backing. I'm not sure if that would cause a serious problem but it seems untidy,
and it doesn't happen in other situations (i.e. with separate memory backend
objects, QEMU sets up the policy specifically for each one and other
allocations aren't affected, AFAIK). Presumably, if memory were very
restricted it could prevent the guest from starting.
Yes, it is, that's what <numatune><memory/> does if you don't have
any
other (<memnode/>) specifics set.
> >I think QEMU could be altered to move the preallocations into
the VCPU
> >threads but it didn't seem trivial and I suspected the QEMU community would
> >point out that there was already a way to do it using backend objects. Another
> >option would be to add a -host-nodes parameter to QEMU so that the policy can
> >be given without adding a memory backend object. (That seems like a more
> >reasonable change to QEMU.)
> >
>
> I think upstream won't like that, mostly because there is already a
> way. And that is using memory-backend object. I think we could just
> use that and disable changing it live. But upstream will probably want
> that to be configurable or something.
Right, but isn't this already an issue in the cases where libvirt is already
using memory backend objects and NUMA policy? (Or does libvirt already disable
changing it live in those situations?)
It is. I'm not trying to say libvirt is perfect. There are bugs,
e.g. like this one. The problem is that we tried to do *everything*,
but it's not currently possible. I'm trying to explain how stuff works
now. It definitely needs some fixing, though.
9:10 p.m.
On Tue, Oct 18, 2016 at 10:43:31PM +0200, Martin Kletzander wrote:
On Mon, Oct 17, 2016 at 03:45:09PM +1100, Sam Bobroff wrote:
>On Fri, Oct 14, 2016 at 10:19:42AM +0200, Martin Kletzander wrote:
>>On Fri, Oct 14, 2016 at 11:52:22AM +1100, Sam Bobroff wrote:
>>>I did look at the libnuma and cgroups approaches, but I was concerned they
>>>wouldn't work in this case, because of the way QEMU allocates memory
when
>>>mem-prealloc is used: the memory is allocated in the main process, before
the
>>>CPU threads are created. (This is based only on a bit of hacking and
debugging
>>>in QEMU, but it does seem explain the behaviour I've seen so far.)
>>>
>>
>>But we use numactl before QEMU is exec()'d.
>
>Sorry, I jumped ahead a bit. I'll try to explain what I mean:
>
>I think the problem with using this method would be that the NUMA policy is
>applied to all allocations by QEMU, not just ones related to the memory
>backing. I'm not sure if that would cause a serious problem but it seems untidy,
>and it doesn't happen in other situations (i.e. with separate memory backend
>objects, QEMU sets up the policy specifically for each one and other
>allocations aren't affected, AFAIK). Presumably, if memory were very
>restricted it could prevent the guest from starting.
>
Yes, it is, that's what <numatune><memory/> does if you don't have
any
other (<memnode/>) specifics set.
>>>I think QEMU could be altered to move the preallocations into the VCPU
>>>threads but it didn't seem trivial and I suspected the QEMU community
would
>>>point out that there was already a way to do it using backend objects.
Another
>>>option would be to add a -host-nodes parameter to QEMU so that the policy
can
>>>be given without adding a memory backend object. (That seems like a more
>>>reasonable change to QEMU.)
>>>
>>
>>I think upstream won't like that, mostly because there is already a
>>way. And that is using memory-backend object. I think we could just
>>use that and disable changing it live. But upstream will probably want
>>that to be configurable or something.
>
>Right, but isn't this already an issue in the cases where libvirt is already
>using memory backend objects and NUMA policy? (Or does libvirt already disable
>changing it live in those situations?)
>
It is. I'm not trying to say libvirt is perfect. There are bugs,
e.g. like this one. The problem is that we tried to do *everything*,
but it's not currently possible. I'm trying to explain how stuff works
now. It definitely needs some fixing, though.
OK :-)
Well, given our discussion, do you think it's worth a v2 of my original patch
or would it be better to drop it in favour of some broader change?
Cheers,
Sam.
7:13 a.m.
On Tue, Oct 25, 2016 at 01:10:23PM +1100, Sam Bobroff wrote:
On Tue, Oct 18, 2016 at 10:43:31PM +0200, Martin Kletzander wrote:
> On Mon, Oct 17, 2016 at 03:45:09PM +1100, Sam Bobroff wrote:
> >On Fri, Oct 14, 2016 at 10:19:42AM +0200, Martin Kletzander wrote:
> >>On Fri, Oct 14, 2016 at 11:52:22AM +1100, Sam Bobroff wrote:
> >>>I did look at the libnuma and cgroups approaches, but I was concerned
they
> >>>wouldn't work in this case, because of the way QEMU allocates memory
when
> >>>mem-prealloc is used: the memory is allocated in the main process, before
the
> >>>CPU threads are created. (This is based only on a bit of hacking and
debugging
> >>>in QEMU, but it does seem explain the behaviour I've seen so far.)
> >>>
> >>
> >>But we use numactl before QEMU is exec()'d.
> >
> >Sorry, I jumped ahead a bit. I'll try to explain what I mean:
> >
> >I think the problem with using this method would be that the NUMA policy is
> >applied to all allocations by QEMU, not just ones related to the memory
> >backing. I'm not sure if that would cause a serious problem but it seems
untidy,
> >and it doesn't happen in other situations (i.e. with separate memory backend
> >objects, QEMU sets up the policy specifically for each one and other
> >allocations aren't affected, AFAIK). Presumably, if memory were very
> >restricted it could prevent the guest from starting.
> >
>
> Yes, it is, that's what <numatune><memory/> does if you don't
have any
> other (<memnode/>) specifics set.
>
> >>>I think QEMU could be altered to move the preallocations into the VCPU
> >>>threads but it didn't seem trivial and I suspected the QEMU community
would
> >>>point out that there was already a way to do it using backend objects.
Another
> >>>option would be to add a -host-nodes parameter to QEMU so that the policy
can
> >>>be given without adding a memory backend object. (That seems like a more
> >>>reasonable change to QEMU.)
> >>>
> >>
> >>I think upstream won't like that, mostly because there is already a
> >>way. And that is using memory-backend object. I think we could just
> >>use that and disable changing it live. But upstream will probably want
> >>that to be configurable or something.
> >
> >Right, but isn't this already an issue in the cases where libvirt is already
> >using memory backend objects and NUMA policy? (Or does libvirt already disable
> >changing it live in those situations?)
> >
>
> It is. I'm not trying to say libvirt is perfect. There are bugs,
> e.g. like this one. The problem is that we tried to do *everything*,
> but it's not currently possible. I'm trying to explain how stuff works
> now. It definitely needs some fixing, though.
OK :-)
Well, given our discussion, do you think it's worth a v2 of my original patch
or would it be better to drop it in favour of some broader change?
Honestly, I thought about the approaches so much I'm now not sure I'll
make a good decision. RFC could do. If I were to pick, I would go with
a new setting that would control whether we want the binding to be
changeable throughout the domain's lifetime or not so that we can make
better decisions (and don't feel bad about the bad ones).
Cheers,
Sam.
11:15 p.m.
On Tue, Oct 25, 2016 at 02:13:07PM +0200, Martin Kletzander wrote:
On Tue, Oct 25, 2016 at 01:10:23PM +1100, Sam Bobroff wrote:
>On Tue, Oct 18, 2016 at 10:43:31PM +0200, Martin Kletzander wrote:
>>On Mon, Oct 17, 2016 at 03:45:09PM +1100, Sam Bobroff wrote:
>>>On Fri, Oct 14, 2016 at 10:19:42AM +0200, Martin Kletzander wrote:
>>>>On Fri, Oct 14, 2016 at 11:52:22AM +1100, Sam Bobroff wrote:
>>>>>I did look at the libnuma and cgroups approaches, but I was concerned
they
>>>>>wouldn't work in this case, because of the way QEMU allocates
memory when
>>>>>mem-prealloc is used: the memory is allocated in the main process,
before the
>>>>>CPU threads are created. (This is based only on a bit of hacking and
debugging
>>>>>in QEMU, but it does seem explain the behaviour I've seen so
far.)
>>>>>
>>>>
>>>>But we use numactl before QEMU is exec()'d.
>>>
>>>Sorry, I jumped ahead a bit. I'll try to explain what I mean:
>>>
>>>I think the problem with using this method would be that the NUMA policy is
>>>applied to all allocations by QEMU, not just ones related to the memory
>>>backing. I'm not sure if that would cause a serious problem but it seems
untidy,
>>>and it doesn't happen in other situations (i.e. with separate memory
backend
>>>objects, QEMU sets up the policy specifically for each one and other
>>>allocations aren't affected, AFAIK). Presumably, if memory were very
>>>restricted it could prevent the guest from starting.
>>>
>>
>>Yes, it is, that's what <numatune><memory/> does if you don't
have any
>>other (<memnode/>) specifics set.
>>
>>>>>I think QEMU could be altered to move the preallocations into the
VCPU
>>>>>threads but it didn't seem trivial and I suspected the QEMU
community would
>>>>>point out that there was already a way to do it using backend
objects. Another
>>>>>option would be to add a -host-nodes parameter to QEMU so that the
policy can
>>>>>be given without adding a memory backend object. (That seems like a
more
>>>>>reasonable change to QEMU.)
>>>>>
>>>>
>>>>I think upstream won't like that, mostly because there is already a
>>>>way. And that is using memory-backend object. I think we could just
>>>>use that and disable changing it live. But upstream will probably want
>>>>that to be configurable or something.
>>>
>>>Right, but isn't this already an issue in the cases where libvirt is
already
>>>using memory backend objects and NUMA policy? (Or does libvirt already
disable
>>>changing it live in those situations?)
>>>
>>
>>It is. I'm not trying to say libvirt is perfect. There are bugs,
>>e.g. like this one. The problem is that we tried to do *everything*,
>>but it's not currently possible. I'm trying to explain how stuff works
>>now. It definitely needs some fixing, though.
>
>OK :-)
>
>Well, given our discussion, do you think it's worth a v2 of my original patch
>or would it be better to drop it in favour of some broader change?
>
Honestly, I thought about the approaches so much I'm now not sure I'll
make a good decision. RFC could do. If I were to pick, I would go with
a new setting that would control whether we want the binding to be
changeable throughout the domain's lifetime or not so that we can make
better decisions (and don't feel bad about the bad ones).
I feel the same way.
OK, I'll try an RFC patch with a lot of description.
I'm specifically trying to address the issue I originally raised, which isn't
quite the same thing as the changeability of the bindings but I'll keep that in
mind. I think your point about changing the bindings will apply in the
same way whenever QEMU's memory-backend objects are used with their
"host-nodes" attribute (since they are what causes QEMU to apply policy), so I
don't think I'm suggesting any significant change there.
If you want to add the new setting you mention above, I'd be happy to base my
patch of top of that work. ;-)
Cheers,
Sam.
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