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 16:32:25 -0700
From:   Vikram Mulukutla <markivx@...eaurora.org>
To:     qiaozhou <qiaozhou@...micro.com>
Cc:     Will Deacon <will.deacon@....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 Qiao,


On 2017-08-01 00:37, qiaozhou wrote:
> On 2017年07月31日 19:20, qiaozhou wrote:
>> 
>> 

<snip>

>>> =====================================================
>>> Also apply Vikram's patch and have a test.
> 
> cpu2: a53, 832MHz, cpu7: a73, 1.75Hz
> Without cpu_relax bodging patch
> =====================================================
> cpu2 time | cpu2 counter | cpu7 time | cpu7 counter |
> ==========|==============|===========|==============|
>      16505|          5243|          2|      12487322|
>      16494|          5619|          1|      12013291|
>      16498|          5276|          2|      11706824|
>      16494|          7123|          1|      12532355|
>      16470|          7208|          2|      11784617|
> =====================================================
> 
> cpu2: a53, 832MHz, cpu7: a73, 1.75Hz
> With cpu_relax bodging patch:
> =====================================================
> cpu2 time | cpu2 counter | cpu7 time | cpu7 counter |
> ==========|==============|===========|==============|
>       3991|        140714|          1|      11430528|
>       4018|        144371|          1|      11430528|
>       4034|        143250|          1|      11427011|
>       4330|        147345|          1|      11423583|
>       4752|        138273|          1|      11433241|
> =====================================================
> 
> It has some improvements, but not so good as Vikram's data. The big
> core still has much more chance to acquire lock.
>>> 
>>> Thanks,
>>> Vikram
>>> 

Thanks for your data! I'll check on one of our other platforms to see
if I see similar behavior. This may have something to do with the
event-stream on your platform or the A53 revision as Sudeep pointed
out here [1] - something to check I suppose...

Thanks,
Vikram

[1] - https://lkml.org/lkml/2016/11/21/458

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