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Re: [Qemu-devel] [PATCH] spapr: clock should count only if vm is running

From: Laurent Vivier
Subject: Re: [Qemu-devel] [PATCH] spapr: clock should count only if vm is running
Date: Fri, 27 Jan 2017 10:23:42 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 27/01/2017 09:52, Paolo Bonzini wrote:
>> This is a port to ppc of the i386 commit:
>>     00f4d64 kvmclock: clock should count only if vm is running
>> We remove timebase_/pre_save/post_load/ functions,
>> and use the VM state change handler to save and restore
>> the guest_timebase (on stop and continue).
>> Time base offset has originally been introduced by commit
>>     98a8b52 spapr: Add support for time base offset migration
>> So while VM is paused, the time is stopped. This allows to have
>> the same result with date (based on Time Base Register) and
>> hwclock (based on "get-time-of-day" RTAS call).
>> Moreover in TCG mode, the Time Base is always paused, so this
>> patch also adjust the behavior between TCG and KVM.
>> VM state field "time_of_the_day_ns" is now useless but we keep
>> it to be able to migrate to older version of the machine.
>> As vmstate_ppc_timebase structure (with timebase_pre_save() and
>> timebase_post_load() functions) was only used by vmstate_spapr,
>> we register the VM state change handler only in ppc_spapr_init().
>> Signed-off-by: Laurent Vivier <address@hidden>
> I think you should keep the pre_save handler, otherwise after
> migration the timebase register will be off by as long as the
> time needed to do the final RAM transfer.  See commit 6053a86
> ("kvmclock: reduce kvmclock difference on migration", 2016-12-22).

I will.

Thank you,

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