linux-kernel - Re: [PATCH v4 1/2] KVM: LAPIC: Optimize timer latency consider world switch time

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Message-ID: <CANRm+CyykkkvCP0sS6SBOMO_XFYVviOGNcQOMuudGZ3y0y1YQg@mail.gmail.com>
Date:   Thu, 4 Jul 2019 08:37:44 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v4 1/2] KVM: LAPIC: Optimize timer latency consider world
 switch time

On Wed, 3 Jul 2019 at 22:13, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 03/07/19 02:48, Wanpeng Li wrote:
> > Hi Paolo, how about this patchset? Patch 2/2 is easy to take, do you
> > have more concern about patch 1/2?
>
> I don't know.  It seems somewhat hard to tune and in cyclictest it only
> happens for preemption_timer=N.  Are you using preemption_timer=N
> together with the LAPIC-timer-on-service-CPU patches?

A 25ns conservative value makes no benefit for cyclictest any more
even when preemption_timer=N. Btw, maybe it is the time to merge the
LAPIC-timer-on-service-CPU patches now. :)

Regards,
Wanpeng Li