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

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Date:   Thu, 03 Aug 2017 16:25:12 -0700
From:   Vikram Mulukutla <markivx@...eaurora.org>
To:     Will Deacon <will.deacon@....com>
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 Will,

On 2017-07-31 06:13, Will Deacon wrote:
> Hi Vikram,
> 
> 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.

Thanks,
Vikram
-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project