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Date: Thu, 03 Aug 2017 16:25:12 -0700
From: Vikram Mulukutla <markivx@codeaurora.org>
To: Will Deacon <will.deacon@arm.com>
Cc: qiaozhou <qiaozhou@asrmicro.com>, Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>, sboyd@codeaurora.org,
        LKML <linux-kernel@vger.kernel.org>,
        Wang Wilbur <wilburwang@asrmicro.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel-owner@vger.kernel.org, sudeep.holla@arm.com
Subject: Re: [Question]: try to fix contention between expire_timers and
 try_to_del_timer_sync
In-Reply-To: <20170731131321.GB1737@arm.com>
References: <3d2459c7-defd-a47e-6cea-007c10cecaac@asrmicro.com>
 <alpine.DEB.2.20.1707261548560.2186@nanos>
 <dcb18367-c747-96a8-9927-d8ba6954c496@asrmicro.com>
 <e1cc02c5e7dfd4d6bec937b6dc97bfc7@codeaurora.org>
 <20170728092831.GA24839@arm.com>
 <2aa9684cf9c889ee9fdc8550b4388af6@codeaurora.org>
 <20170731131321.GB1737@arm.com>
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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
-- 
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