[PATCH v2] KVM: X86: Limit timer frequency to 200ms

[PATCH v2] KVM: X86: Limit timer frequency to 200ms

[Wanpeng Li]

From: Wanpeng Li <wanpengli@tencent.com>

Anthoine reported:
 The period used by Windows change over time but it can be 1 milliseconds
 or less. I saw the limit_periodic_timer_frequency print so 500
 microseconds is sometimes reached.

As suggested by Paolo, lower the timer frequency limit to a
smaller interval of 200 ms (5000 Hz) to leave some headroom. This
is required due to Windows 10 changing the scheduler tick limit
from 1024 Hz to 2048 Hz.

Reported-by: Anthoine Bourgeois <anthoine.bourgeois@blade-group.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com> 
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Anthoine Bourgeois <anthoine.bourgeois@blade-group.com>
Cc: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
v1 -> v2:
 * update patch subject and description

 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 51ecd38..dc47073 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -114,7 +114,7 @@ module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
 static bool __read_mostly report_ignored_msrs = true;
 module_param(report_ignored_msrs, bool, S_IRUGO | S_IWUSR);
 
-unsigned int min_timer_period_us = 500;
+unsigned int min_timer_period_us = 200;
 module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
 
 static bool __read_mostly kvmclock_periodic_sync = true;
-- 
2.7.4

Re: [PATCH v2] KVM: X86: Limit timer frequency to 200ms

[Wanpeng Li]

ping,
2018-05-01 7:35 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Anthoine reported:
>  The period used by Windows change over time but it can be 1 milliseconds
>  or less. I saw the limit_periodic_timer_frequency print so 500
>  microseconds is sometimes reached.
>
> As suggested by Paolo, lower the timer frequency limit to a
> smaller interval of 200 ms (5000 Hz) to leave some headroom. This
> is required due to Windows 10 changing the scheduler tick limit
> from 1024 Hz to 2048 Hz.
>
> Reported-by: Anthoine Bourgeois <anthoine.bourgeois@blade-group.com>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Anthoine Bourgeois <anthoine.bourgeois@blade-group.com>
> Cc: Darren Kenny <darren.kenny@oracle.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v1 -> v2:
>  * update patch subject and description
>
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 51ecd38..dc47073 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -114,7 +114,7 @@ module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
>  static bool __read_mostly report_ignored_msrs = true;
>  module_param(report_ignored_msrs, bool, S_IRUGO | S_IWUSR);
>
> -unsigned int min_timer_period_us = 500;
> +unsigned int min_timer_period_us = 200;
>  module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
>
>  static bool __read_mostly kvmclock_periodic_sync = true;
> --
> 2.7.4
>

Re: [PATCH v2] KVM: X86: Limit timer frequency to 200ms

[Jan Kiszka]

On 2018-05-05 01:44, Wanpeng Li wrote:
> ping,
> 2018-05-01 7:35 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
>> From: Wanpeng Li <wanpengli@tencent.com>
>>
>> Anthoine reported:
>>  The period used by Windows change over time but it can be 1 milliseconds
>>  or less. I saw the limit_periodic_timer_frequency print so 500
>>  microseconds is sometimes reached.
>>
>> As suggested by Paolo, lower the timer frequency limit to a
>> smaller interval of 200 ms (5000 Hz) to leave some headroom. This
>> is required due to Windows 10 changing the scheduler tick limit
>> from 1024 Hz to 2048 Hz.

"... lower the *default* timer frequency limit to a smaller interval of
200 *us* ..." - same for the subject.

(Amazing that even Windows 10 still uses periodic ticks.)

Jan

>>
>> Reported-by: Anthoine Bourgeois <anthoine.bourgeois@blade-group.com>
>> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
>> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Cc: Anthoine Bourgeois <anthoine.bourgeois@blade-group.com>
>> Cc: Darren Kenny <darren.kenny@oracle.com>
>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
>> ---
>> v1 -> v2:
>>  * update patch subject and description
>>
>>  arch/x86/kvm/x86.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 51ecd38..dc47073 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -114,7 +114,7 @@ module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
>>  static bool __read_mostly report_ignored_msrs = true;
>>  module_param(report_ignored_msrs, bool, S_IRUGO | S_IWUSR);
>>
>> -unsigned int min_timer_period_us = 500;
>> +unsigned int min_timer_period_us = 200;
>>  module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
>>
>>  static bool __read_mostly kvmclock_periodic_sync = true;
>> --
>> 2.7.4
>>
> 

Re: [PATCH v2] KVM: X86: Limit timer frequency to 200ms

[Wanpeng Li]

2018-05-05 16:36 GMT+08:00 Jan Kiszka <jan.kiszka@web.de>:
> On 2018-05-05 01:44, Wanpeng Li wrote:
>> ping,
>> 2018-05-01 7:35 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
>>> From: Wanpeng Li <wanpengli@tencent.com>
>>>
>>> Anthoine reported:
>>>  The period used by Windows change over time but it can be 1 milliseconds
>>>  or less. I saw the limit_periodic_timer_frequency print so 500
>>>  microseconds is sometimes reached.
>>>
>>> As suggested by Paolo, lower the timer frequency limit to a
>>> smaller interval of 200 ms (5000 Hz) to leave some headroom. This
>>> is required due to Windows 10 changing the scheduler tick limit
>>> from 1024 Hz to 2048 Hz.
>
> "... lower the *default* timer frequency limit to a smaller interval of
> 200 *us* ..." - same for the subject.

Thanks Jan, I will update it.

Regards,
Wanpeng Li