On Mon, 10 Sep 2018 14:49:23 -0300 Eduardo Habkost <ehabkost@redhat.com> wrote:
On Thu, Sep 06, 2018 at 10:02:13AM +0200, Igor Mammedov wrote:
On Wed, 5 Sep 2018 10:45:12 -0300 Eduardo Habkost <ehabkost@redhat.com> wrote:
On Wed, Sep 05, 2018 at 11:25:11AM +0200, Igor Mammedov wrote:
On Tue, 4 Sep 2018 23:12:55 -0300 Eduardo Habkost <ehabkost@redhat.com> wrote:
On Tue, Sep 04, 2018 at 03:22:35PM +0200, Igor Mammedov wrote:
-smp [cpus],sockets/cores/threads[,maxcpus] should describe topology so that total number of logical CPUs [sockets * cores * threads] would be equal to [maxcpus], however historically we didn't have such check in QEMU and it is possible to start VM with an invalid topology. Deprecate invalid options combination so we can make sure that the topology VM started with is always correct in the future. Users with an invalid sockets/cores/threads/maxcpus values should fix their CLI to make sure that [sockets * cores * threads] == [maxcpus]
Signed-off-by: Igor Mammedov <imammedo@redhat.com> --- v5: - extend deprecation doc, adding that maxcpus should be multiple of present on CLI [sockets/cores/threads] options (Eduardo Habkost <ehabkost@redhat.com>) v4: - missed dot comment, fix it with s/./,/ (Andrew Jones <drjones@redhat.com>) v3: - more spelling fixes (Andrew Jones <drjones@redhat.com>) - place deprecation check after (sockets * cores * threads > max_cpus) check (Eduardo Habkost <ehabkost@redhat.com>) v2: - spelling&&co fixes (Andrew Jones <drjones@redhat.com>) --- qemu-deprecated.texi | 19 +++++++++++++++++++ vl.c | 7 +++++++ 2 files changed, 26 insertions(+)
diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi index 87212b6..827c3ce 100644 --- a/qemu-deprecated.texi +++ b/qemu-deprecated.texi @@ -159,6 +159,25 @@ The 'file' driver for drives is no longer appropriate for character or host devices and will only accept regular files (S_IFREG). The correct driver for these file types is 'host_cdrom' or 'host_device' as appropriate.
+@subsection -smp X,[socket=a,core=b,thread=c],maxcpus=Y (since 3.1)
Minor: I suggest using @var markup, or maybe just use "-smp (invalid topologies) (since 3.1)" as subsection title for simplicity?
+ +CPU topology properties should describe whole machine topology including +possible CPUs, but historically it was possible to start QEMU with +an incorrect topology where + sockets * cores * threads >= X && X < maxcpus
Minor: this line formatting is lost on the HTML output. I suggest using @var and/or @math.
Minor: I suggest not using C syntax.
i.e. use something like:
@math{@var{n} <= @var{sockets} * @var{cores} * @var{threads} < @var{maxcpus}},
+which could lead to an incorrect topology enumeration by the guest. +Support for invalid topologies will be removed, the user must ensure +topologies described with -smp include all possible cpus, i.e. + sockets * cores * threads == maxcpus
Minor: same as above. I suggest:
@math{@var{sockets} * @var{cores} * @var{threads} = @var{maxcpus}}.
+Note: it's assumed that maxcpus value must be multiple of the topology +options present on command line to avoid creating an invalid topology. +If maxcpus isn't be multiple of present topology options then the condition +(sockets * cores * threads == maxcpus) can't be satisfied and it will +trigger deprecation warning which later will be converted to a error. +If you get deprecation warning it's recommended to explicitly specify +a correct topology to make warning go away and ensure that it will +continue working in the future.
I don't understand the purpose of the "Note:" section. It seems to duplicate what was already said in the lines above it. Can we just remove it? Well, didn't I say that no additional explanation needed in v4? Note section was added per your suggestion to explicitly say that maxcpus should be multiple of options present on CLI.
You are right: I did ask for additional clarification on the documentation, because it was not clear that the warning can still appear even if some of the sockets/cores/threads options were omitted. The note didn't make that clearer to me, though. I can respin if necessary (we are not in hurry so no need to merge something that would be removed immediately). Could you suggest a text for clarification for me to include on respin?
I was planning to write a suggestion later, but I didn't want this series to be delayed because of me. Just removing the existing "Notes:" section would be good enough to me.
Probably the right place to document the subtle details of the s/c/t/maxcpus requirements is the "-smp" section on qemu-options.hx, not qemu-deprecated.hx.
I was considering something like this:
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> --- diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi index 060e015be6..74f6a64b8b 100644 --- a/qemu-deprecated.texi +++ b/qemu-deprecated.texi @@ -139,16 +139,20 @@ The 'file' driver for drives is no longer appropriate for character or host devices and will only accept regular files (S_IFREG). The correct driver for these file types is 'host_cdrom' or 'host_device' as appropriate.
-@subsection -smp X,[socket=a,core=b,thread=c],maxcpus=Y (since 3.1) +@subsection -smp (invalid topologies) (since 3.1)
CPU topology properties should describe whole machine topology including -possible CPUs, but historically it was possible to start QEMU with +possible CPUs. In other words: @var{maxcpus} should be equal to +@math{@var{sockets} * @var{cores} * @var{threads}}. + +However, historically it was possible to start QEMU with an incorrect topology where - sockets * cores * threads >= X && X < maxcpus +@math{@var{n} <= @var{sockets} * @var{cores} * @var{threads} < @var{maxcpus}}, which could lead to an incorrect topology enumeration by the guest. Support for invalid topologies will be removed, the user must ensure topologies described with -smp include all possible cpus, i.e. - sockets * cores * threads == maxcpus +@math{@var{sockets} * @var{cores} * @var{threads} = @var{maxcpus}}. + Thanks, suggestions taken in account and I'll drop Note section
@section QEMU Machine Protocol (QMP) commands
diff --git a/qemu-options.hx b/qemu-options.hx index 654ef484d9..2afa271570 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -155,8 +155,13 @@ to 4. For the PC target, the number of @var{cores} per socket, the number of @var{threads} per cores and the total number of @var{sockets} can be specified. Missing values will be computed. If any on the three values is -given, the total number of CPUs @var{n} can be omitted. @var{maxcpus} -specifies the maximum number of hotpluggable CPUs. +given, the total number of CPUs @var{n} can be omitted. + +@var{maxcpus} specifies the maximum number of hotpluggable CPUs +and should be equal to @math{@var{sockets} * @var{cores} * @var{threads}} +(even if @var{sockets}, @var{cores}, or @var{threads} is omitted +and computed automatically). Options doc I've left out, it probably should be separate patch.
ETEXI
DEF("numa", HAS_ARG, QEMU_OPTION_numa,