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

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Message-ID: <164634c5-32df-4542-9a5a-2b357e10a67e@oracle.com>
Date: Wed, 13 Nov 2024 13:22:54 -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: [External] : Re: [REGRESSION] sched/fair: Add lag based placement




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
>>
>>
>>
>>
>>
>>
>>
>>