Re: [libvirt] [PATCHv2 6/6] qemu: refresh vcpu halted state only via query-cpus-fast
On 03/05/2018 06:44 AM, Viktor Mihajlovski wrote:
In order to not affect running VMs, refreshing the halted state
is only performed if QEMU supports the query-cpus-fast QAPI.
Signed-off-by: Viktor Mihajlovski <mihajlov(a)linux.vnet.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy(a)linux.vnet.ibm.com>
Reviewed-by: Marc Hartmayer <mhartmay(a)linux.vnet.ibm.com>
---
src/qemu/qemu_domain.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
BTW: You'll need a patch to docs/news.xml as this is something
newsworthy I would think. Although calling it "-fast" there may make
people wonder about the "slowness" aspect of the current algorithm.
diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 4079fb3..a5fcf22 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -8801,8 +8801,13 @@ qemuDomainRefreshVcpuHalted(virQEMUDriverPtr driver,
return 0;
/* The halted state is interresting only on s390(x). On other platforms
"interesting"
- * the data would be stale at the time when it would be used.
*/
- if (!ARCH_IS_S390(vm->def->os.arch))
+ * the data would be stale at the time when it would be used.
+ * Calling qemuMonitorGetCpuHalted() can adversely affect the running
+ * VM's performance unless QEMU supports query-cpus-fast.
+ */
+ if (!ARCH_IS_S390(vm->def->os.arch) ||
+ !virQEMUCapsGet(QEMU_DOMAIN_PRIVATE(vm)->qemuCaps,
+ QEMU_CAPS_QUERY_CPUS_FAST))
So IOW systems that reported this previously that don't get the updated
QEMU bits (e.g. > 2.12) would now stop reporting halted only because of
the adverse performance impact.
But that is a data change and "policy" we'd be inflicting upon them
which maybe they don't care about. Perhaps in that case we should have a
"flag" that handles whether the caller cares or not.
I understand the motivation and reasoning; however, based on how such
things have been historically acked or nacked, I'm leaning towards
saying this patch shouldn't go in.
John
return 0;
if (qemuDomainObjEnterMonitorAsync(driver, vm, asyncJob) < 0)