linux-kernel - Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer

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Date:   Mon, 6 Jan 2020 14:21:13 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, kvm <kvm@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target()

Hi Thomas,
On Wed, 23 Oct 2019 at 16:29, Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Wed, 23 Oct 2019, Wanpeng Li wrote:
> > I didn't see your refactor to get_nohz_timer_target() which you
> > mentioned in IRC after four months, I can observe cyclictest drop from
> > 4~5us to 8us in kvm guest(we offload the lapic timer emulation to
> > housekeeping cpu to avoid timer fire external interrupt on the pCPU
> > which vCPU resident incur a vCPU vmexit) w/o this patch in the case of
> > there is no busy housekeeping cpu. The score can be recovered after I
> > give stress to create a busy housekeeping cpu.
> >
> > Could you consider applying this patch for temporary since I'm not
> > sure when the refactor can be ready.
>
> Yeah. It's delayed (again).... Will pick that up.

I didn't find WIP tag for this work after ~half year since v4 was
posted https://lkml.org/lkml/2019/6/28/231 Could you apply this patch
for temporary because the completion time of refactor is not
deterministic.

    Wanpeng