linux-kernel - Re: [REGRESSION] sched/fair: Add lag based placement

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Message-ID: <1c447727-92ed-416c-bca1-a7ca0974f0df@oracle.com>
Date: Wed, 13 Nov 2024 13:33:55 -0500
From: Joseph Salisbury <joseph.salisbury@...cle.com>
To: Phil Auld <pauld@...hat.com>
Cc: peterz@...radead.org, mingo@...nel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        Steven Rostedt <rostedt@...dmis.org>, bsegall@...gle.com,
        mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] sched/fair: Add lag based placement




On 11/13/24 13:22, Joseph Salisbury wrote:
>
>
>
> On 11/13/24 13:19, Phil Auld wrote:
>> Hi,
>>
>> On Wed, Nov 13, 2024 at 01:03:00PM -0500 Joseph Salisbury wrote:
>>> Hello,
>>>
>>> During performance testing, we found a regression of ~9% performance 
>>> with
>>> the TPCC benchmark.   This performance regression was introduced in
>>> v6.6-rc1.  After a bisect, the following commit was identified as 
>>> the cause
>>> of the regression:
>>>
>>> 86bfbb7ce4f6 ("sched/fair: Add lag based placement")
>>>
>>> I was hoping to get some feedback from the scheduler folks. Do you 
>>> think
>>> gathering any additional data will help diagnose this issue? Are 
>>> there any
>>> tunable options that can changed to see how performance is affected?
>>>
>> You can try turning off the PLACE_LAG sched feature:
>>
>>      echo NO_PLACE_LAG > /sys/kernel/debug/sched/features
>>
>> It's not what I'd call a tunable but it would allow you to test w/o 
>> it and
>> see what it does.  It should allow you to switch back and forth 
>> easily for
>> testing.
>>
>>
>> Cheers,
>> Phil
> Thanks so much for the suggestion, Phil!  I will give that a try and 
> report the results.
>>
>>> Thanks,
>>>
>>> Joe
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>
>
I just noticed this thread, which is probably related:
https://lore.kernel.org/lkml/ZxuujhhrJcoYOdMJ@BLRRASHENOY1.amd.com/T/