linux-kernel - Re: [PATCH v2 6/8] sched/idle: Move busy

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Date:   Tue, 18 May 2021 14:05:56 +0800
From:   Aubrey Li <aubrey.li@...ux.intel.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Parth Shah <parth@...ux.ibm.com>
Subject: Re: [PATCH v2 6/8] sched/idle: Move busy_cpu accounting to idle
 callback

On 5/18/21 12:00 PM, Srikar Dronamraju wrote:
> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-18 08:59:00]:
> 
>> On 5/17/21 8:57 PM, Srikar Dronamraju wrote:
>>> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-17 20:48:46]:
>>>
>>>> On 5/17/21 6:40 PM, Srikar Dronamraju wrote:
>>>>> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-14 12:11:50]:
>>>>>
>>>>>> On 5/13/21 3:31 PM, Srikar Dronamraju wrote:
>>>>>>> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-12 16:08:24]:
>>>>>>>> On 5/7/21 12:45 AM, Srikar Dronamraju wrote:
>>>>>
>>>>> <snip>
>>>>>
>>>>>>>> Also, for those frequent context-switching tasks with very short idle,
>>>>>>>> it's expensive for scheduler to mark idle/busy every time, that's why
>>>>>>>> my patch only marks idle every time and marks busy ratelimited in
>>>>>>>> scheduler tick.
>>>>>>>>
>>>>>>>
>>>>>>> I have tried few tasks with very short idle times and updating nr_busy
>>>>>>> everytime, doesnt seem to be impacting. Infact, it seems to help in picking
>>>>>>> the idler-llc more often.
>>>>>>>
>>>>>>
>>>>>> How many CPUs in your LLC?
>>>>>
>>>>> I have tried with X86, 48 CPUs, 2 nodes, each having 24 CPUs in LLC
>>>>> +
>>>>> POWER10, Multiple CPUs with 4 CPUs in LLC
>>>>> +
>>>>> POWER9, Multiple CPUs with 8 CPUs in LLC
>>>>>
>>>>>>
>>>>>> This is a system with 192 CPUs, 4 nodes and each node has 48 CPUs in LLC
>>>>>> domain.
>>>>>>
>>>>>
>>>>> Okay,
>>>>>
>>>>>> It looks like for netperf both TCP and UDP cases have the notable change
>>>>>> under 2 x overcommit, it may be not interesting though.
>>>>>>
>>>>>>
>>>>>
>>>>> I believe the extra load on this 24 core LLC could be because we may end up
>>>>> trying to set the idle-core, even when there is no idle core available.
>>>>>
>>>>> If possible, can you please give a try with v3 with the call to
>>>>> set_next_idle_core commented out?
>>>>>
>>>>>
>>>>
>>>> v3 seems not be applicable on tip/sched/core 915a2bc3c6b7?
>>>
>>> I had applied on top of 2ea46c6fc9452ac100ad907b051d797225847e33
>>> which was tag: sched-core-2021-04-28
>>>
>>> The only conflict you get on today's tip is Gautham's one line patch.
>>> Gautham's patch replaced 'this' with 'target'.
>>>
>>> The 2nd patch does away with that line
>>>
>>
>> This is v3. It looks like hackbench gets better. And netperf still has
>> some notable changes under 2 x overcommit cases.
>>
> 
> Thanks Aubrey for the results. netperf (2X) case does seem to regress.
> I was actually expecting the results to get better with overcommit.
> Can you confirm if this was just v3 or with v3 + set_next_idle_core
> disabled?

Do you mean set_idle_cores(not set_next_idle_core) actually? Gautham's patch
changed "this" to "target" in set_idle_cores, and I removed it to apply
v3-2-8-sched-fair-Maintain-the-identity-of-idle-core.patch for tip/sched/core
commit-id 915a2bc3c6b7.