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

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Message-ID: <20241113181930.GD402105@pauld.westford.csb>
Date: Wed, 13 Nov 2024 13:19:30 -0500
From: Phil Auld <pauld@...hat.com>
To: Joseph Salisbury <joseph.salisbury@...cle.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

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,
> 
> Joe
> 
> 
> 
> 
> 
> 
> 
> 

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