Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug

[Wanpeng Li <kernellwp@gmail.com>]

2016-06-06 21:40 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 02/06/2016 15:59, Rik van Riel wrote:
>> If a guest is saved to disk and later restored (eg. after
>> a host reboot), or live migrated to another host, I would
>> expect to get totally disjoint steal time statistics from
>> the "new run" of the guest (which is the same run of the
>> guest OS).
>
> Why?  The preexisting guest steal time is always added to by
> KVM, so the time won't restart from zero.
>
> Continuing the previous count on CPU hot-unplug followed by hot-plug
> is less obvious, but I think it's overall the right thing to do.
>
> In fact, I was going to test a patch this week as simple as this:
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index eea2a6f72b31..1ef5e48b3a36 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -301,8 +301,6 @@ static void kvm_register_steal_time(void)
>         if (!has_steal_clock)
>                 return;
>
> -       memset(st, 0, sizeof(*st));
> -
>         wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
>         pr_info("kvm-stealtime: cpu %d, msr %llx\n",
>                 cpu, (unsigned long long) slow_virt_to_phys(st));

Thanks for the suggestion, I will try it today.

Regards,
Wanpeng Li