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

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Date:   Sat, 5 May 2018 10:36:23 +0200
From:   Jan Kiszka <jan.kiszka@....de>
To:     Wanpeng Li <kernellwp@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Anthoine Bourgeois <anthoine.bourgeois@...de-group.com>,
        Darren Kenny <darren.kenny@...cle.com>
Subject: Re: [PATCH v2] KVM: X86: Limit timer frequency to 200ms

On 2018-05-05 01:44, Wanpeng Li wrote:
> ping,
> 2018-05-01 7:35 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
>> From: Wanpeng Li <wanpengli@...cent.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@...de-group.com>
>> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
>> Reviewed-by: Darren Kenny <darren.kenny@...cle.com>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Anthoine Bourgeois <anthoine.bourgeois@...de-group.com>
>> Cc: Darren Kenny <darren.kenny@...cle.com>
>> Signed-off-by: Wanpeng Li <wanpengli@...cent.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
>>
>