Re: DomU clock jumps forward then freezes after Dom0 reboot

[Jeremy Fitzhardinge <jeremy@goop.org>]

 On 10/26/2010 06:08 AM, Cédric Schieli wrote:
> 2010/10/26 Jeremy Fitzhardinge <jeremy@goop.org>:
>>  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.

OK, thanks very much.

    J

> Thanks !
>
>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>> 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@citrix.com>
>>
>> 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;
>>
>>
>>
>>