Re: 2.6.35-rc1 regression with pvclock and smp guests

Zachary Amsden
2010-10-08T02:47:22Z

On 10/07/2010 02:12 PM, Arjan Koers wrote:
> On 2010-10-03 01:42, Zachary Amsden wrote:
> ...
>
>> Umm... do you guys have this commit? This is supposed to address the
>> issue where the guest keeps resetting the TSC. A guest which does that
>> will break kvmclock. It only happens on SMP, and it's much worse on AMD
>> CPUs...
>>
>> sound like your scenario.
>>
>> commit bd59fc8ff95126f27b7a0df1b6cc602aa428812d
>> Author: Zachary Amsden<zamsden@redhat.com>
>> Date: Thu Aug 19 22:07:26 2010 -1000
>>
>
> This commit fixes the problem:
>
> commit aad07c4f92bae2edaa42bcef84c2afdd0d082458
> Author: Zachary Amsden<zamsden@redhat.com>
> Date: Thu Aug 19 22:07:19 2010 -1000
>
> KVM: x86: Move TSC reset out of vmcb_init
>
> The VMCB is reset whenever we receive a startup IPI, so Linux is setting
> TSC back to zero happens very late in the boot process and destabilizing
> the TSC. Instead, just set TSC to zero once at VCPU creation time.
>
> Why the separate patch? So git-bisect is your friend.
>

Okay, apparently I need to go poke around 2.6.35 and see what patches
made it there and what patches didn't.