Re: 2.6.35-rc1 regression with pvclock and smp guests

Arjan Koers
2010-10-08T00:12:59Z

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.