Re: [Xen-devel] DomU clock jumps forward then freezes after Dom0 reboot

[Cédric Schieli <cschieli@xxxxxxxxx>]

2010/10/26 Jeremy Fitzhardinge <jeremy@xxxxxxxx>:
>  On 10/24/2010 05:31 AM, Cédric Schieli wrote:
>> Hello,
>>
>> I can confirm my problem reported here
>> http://lists.xensource.com/archives/html/xen-devel/2010-10/msg00057.html
>> is the same.
>> DomU kernels affected by the migration hang are also affected by the
>> save/restore hang. Reverting "x86, paravirt: Add a global
>> synchronization point for pvclock" also fix the save/restore hang.
>> After doing save/reboot/restore (which led to a hang), migrating it to
>> a host with a longer uptime will unblock the domain, but the wallclock
>> will be several hours forward. Migrating back will block again.
>
> Does this help?

Yes. With this patch applied I can migrate and migrate back without
problem. Save/restore with a reboot in between also works.

Thanks !

>
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> Date: Mon, 25 Oct 2010 16:53:46 -0700
> Subject: [PATCH] x86/pvclock: zero last_value on resume
>
> If the guest domain has been suspend/resumed or migrated, then the
> system clock backing the pvclock clocksource may revert to a smaller
> value (ie, can be non-monotonic across the migration/save-restore).
> Make sure we zero last_value in that case so that the domain
> continues to see clock updates.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
>
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index cd02f32..6226870 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -11,5 +11,6 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info 
> *src);
>  void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
>                            struct pvclock_vcpu_time_info *vcpu,
>                            struct timespec *ts);
> +void pvclock_resume(void);
>
>  #endif /* _ASM_X86_PVCLOCK_H */
> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
> index 239427c..a4f07c1 100644
> --- a/arch/x86/kernel/pvclock.c
> +++ b/arch/x86/kernel/pvclock.c
> @@ -120,6 +120,11 @@ unsigned long pvclock_tsc_khz(struct 
> pvclock_vcpu_time_info *src)
>
>  static atomic64_t last_value = ATOMIC64_INIT(0);
>
> +void pvclock_resume(void)
> +{
> +       atomic64_set(&last_value, 0);
> +}
> +
>  cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
>  {
>        struct pvclock_shadow_time shadow;
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index b2bb5aa..5da5e53 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -426,6 +426,8 @@ void xen_timer_resume(void)
>  {
>        int cpu;
>
> +       pvclock_resume();
> +
>        if (xen_clockevent != &xen_vcpuop_clockevent)
>                return;
>
>
>
>

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