linux-kernel - Re: [PATCH 4/4] sched/fair: Proportional newidle balance

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Message-ID: <341aef79-43fd-43a6-b5b7-ad4689ba394e@arm.com>
Date: Mon, 10 Nov 2025 14:55:40 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Peter Zijlstra <peterz@...radead.org>, Chris Mason <clm@...a.com>,
 Joseph Salisbury <joseph.salisbury@...cle.com>,
 Adam Li <adamli@...amperecomputing.com>,
 Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>, Josh Don <joshdon@...gle.com>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance

On 07.11.25 17:06, Peter Zijlstra wrote:
> Add a randomized algorithm that runs newidle balancing proportional to
> its success rate.
> 
> This improves schbench significantly:
> 
>  6.18-rc4:			2.22 Mrps/s
>  6.18-rc4+revert:		2.04 Mrps/s
>  6.18-rc4+revert+random:	2.18 Mrps/S
> 
> Conversely, per Adam Li this affects SpecJBB slightly, reducing it by 1%:
> 
>  6.17:			-6%
>  6.17+revert:		 0%
>  6.17+revert+random:	-1%
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Results with OLTP 'hammerdb - mysqld' on Arm64 VMs

				NOPM		P50 latency

6.18-rc4			baseline	baseline

6.18-rc4+revert-155213a2aed4	+13%		-8.8%

6.18-rc4+patchset		+11%		-8.2%

6.18-rc4+patchset+NO_NI_RANDOM	+13%		-8.6%

Pretty consistent with the results on the previous version. Although I
hadn't tested NI_TARGET+NI_RANDOM back then.

http://lkml.kernel.org/r/f6379aa6-459d-4205-96ea-9848e55d7f9c@arm.com

In case (pure wakeup) schbench configs are the only workloads profiting
from NI_RANDOM, make NO_NI_RANDOM the default?

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>

[...]