linux-kernel - Re: [PATCH v3] KVM: X86: Lower the default timer frequency limit to 200us

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Message-ID: <2028bdd8-ae0d-1449-b25f-23ae3896e3a3@redhat.com>
Date:   Tue, 15 May 2018 11:57:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Anthoine Bourgeois <anthoine.bourgeois@...de-group.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Jan Kiszka <jan.kiszka@....de>
Subject: Re: [PATCH v3] KVM: X86: Lower the default timer frequency limit to
 200us

On 05/05/2018 13:02, Wanpeng Li wrote:
> 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 default timer frequency limit to a
> smaller interval of 200 us (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@...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>
> Cc: Jan Kiszka <jan.kiszka@....de>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
> v2 -> v3:
>  * update patch subject and description
> 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;
> 

Applied, thanks.

Paolo