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

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Date:   Fri, 4 Aug 2017 11:15:08 +0800
From:   qiaozhou <qiaozhou@...micro.com>
To:     Vikram Mulukutla <markivx@...eaurora.org>
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



On 2017年08月04日 07:32, Vikram Mulukutla wrote:
> 
> 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 for the reminder. Our HW IP has already fixed the bug Sudeep 
mentioned. I'm also checking the global exclusive monitor implementation 
on our platform with our ASIC guys, and it might be related with snoop 
transaction, or implement details in global exclusive monitor.

Thanks a lot.
Qiao
> 
> Thanks,
> Vikram
> 
> [1] - https://lkml.org/lkml/2016/11/21/458
>