linux-kernel - Re: [Question]: try to fix contention between expire_timers and try_to_del_timer

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Date:   Tue, 15 Aug 2017 19:40:40 +0100
From:   Will Deacon <will.deacon@....com>
To:     Vikram Mulukutla <markivx@...eaurora.org>
Cc:     qiaozhou <qiaozhou@...micro.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>, sboyd@...eaurora.org,
        LKML <linux-kernel@...r.kernel.org>,
        Wang Wilbur <wilburwang@...micro.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel-owner@...r.kernel.org, sudeep.holla@....com
Subject: Re: [Question]: try to fix contention between expire_timers and
 try_to_del_timer_sync

Hi Vikram,

On Thu, Aug 03, 2017 at 04:25:12PM -0700, Vikram Mulukutla wrote:
> On 2017-07-31 06:13, Will Deacon wrote:
> >On Fri, Jul 28, 2017 at 12:09:38PM -0700, Vikram Mulukutla wrote:
> >>On 2017-07-28 02:28, Will Deacon wrote:
> >>>On Thu, Jul 27, 2017 at 06:10:34PM -0700, Vikram Mulukutla wrote:
> 
> >>>
> >>This does seem to help. Here's some data after 5 runs with and without
> >>the
> >>patch.
> >
> >Blimey, that does seem to make a difference. Shame it's so ugly! Would you
> >be able to experiment with other values for CPU_RELAX_WFE_THRESHOLD? I had
> >it set to 10000 in the diff I posted, but that might be higher than
> >optimal.
> >It would be interested to see if it correlates with num_possible_cpus()
> >for the highly contended case.
> >
> >Will
> 
> Sorry for the late response - I should hopefully have some more data with
> different thresholds before the week is finished or on Monday.

Did you get anywhere with the threshold heuristic?

Will