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[Qemu-devel] Re: [PATCH v3 07/10] qemu-kvm: Cleanup/fix TSC and PV clock


From: Marcelo Tosatti
Subject: [Qemu-devel] Re: [PATCH v3 07/10] qemu-kvm: Cleanup/fix TSC and PV clock writeback
Date: Wed, 24 Feb 2010 20:17:08 -0300
User-agent: Mutt/1.5.20 (2009-08-17)

On Wed, Feb 24, 2010 at 03:17:55PM +0100, Jan Kiszka wrote:
> Drop kvm_load_tsc in favor of level-dependent writeback in
> kvm_arch_load_regs. KVM's PV clock MSRs fall in the same category and
> should therefore only be written back on full sync.
> 
> Signed-off-by: Jan Kiszka <address@hidden>
> ---
>  qemu-kvm-x86.c        |   19 +++++--------------
>  qemu-kvm.h            |    4 ----
>  target-i386/machine.c |    5 -----
>  3 files changed, 5 insertions(+), 23 deletions(-)
> 
> diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
> index 840c1c9..84fd7fa 100644
> --- a/qemu-kvm-x86.c
> +++ b/qemu-kvm-x86.c
> @@ -965,8 +965,11 @@ void kvm_arch_load_regs(CPUState *env, int level)
>          set_msr_entry(&msrs[n++], MSR_LSTAR  ,           env->lstar);
>      }
>  #endif
> -    set_msr_entry(&msrs[n++], MSR_KVM_SYSTEM_TIME,  env->system_time_msr);
> -    set_msr_entry(&msrs[n++], MSR_KVM_WALL_CLOCK,  env->wall_clock_msr);
> +    if (level == KVM_PUT_FULL_STATE) {
> +        set_msr_entry(&msrs[n++], MSR_IA32_TSC, env->tsc);
> +        set_msr_entry(&msrs[n++], MSR_KVM_SYSTEM_TIME, env->system_time_msr);
> +        set_msr_entry(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
> +    }

As things stand today, the TSC should only be written on migration. See
53f658b3c33616a4997ee254311b335e59063289 in the kernel.





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