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

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Message-ID: <87a76v8knv.fsf@nanos.tec.linutronix.de>
Date:   Fri, 10 Jan 2020 15:12:52 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Wanpeng Li <kernellwp@...il.com>
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()

Wanpeng,

Wanpeng Li <kernellwp@...il.com> writes:

> 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.

Could you please repost it?

Thanks,

        tglx