spapr: Do not re-read the clock on pre_save handler on migration

[Qemu-devel] [PATCH 0/1] spapr: Do not re-read the clock on pre_save handler on migration

Maxiwell S. Garcia posted 1 patch 6 years, 5 months ago

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git fetch https://github.com/patchew-project/qemu tags/patchew/20190520204340.832-1-maxiwell@linux.ibm.com

Maintainers: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/ppc.c | 24 ------------------------
1 file changed, 24 deletions(-)

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[Qemu-devel] [PATCH 0/1] spapr: Do not re-read the clock on pre_save handler on migration

Posted by Maxiwell S. Garcia 6 years, 5 months ago

I suggest to remove the pre_save handler that saves the timebase before
migrate. The commit that added this was ported from x86:
  6053a86fe7bd: kvmclock: reduce kvmclock difference on migration

The review [1] had a discussion about it. The author says that a VM
already paused 10 minutes ago should re-read the clock just before
migrate. But a reviewer question was not answered:

"Is it really valid to make the clock move on an already-paused
VM, only because it was migrated?"

This clock move makes the guest know about the pause between the stop
and migrate commands. Many side effects could happen after migration.

[1] http://lists.nongnu.org/archive/html/qemu-devel/2016-12/msg00610.html

Maxiwell S. Garcia (1):
  spapr: Do not re-read the clock on pre_save handler on migration

 hw/ppc/ppc.c | 24 ------------------------
 1 file changed, 24 deletions(-)

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