linux-kernel - Re: [PATCH 0/2] [tip: sched/core] sched: Disable PLACE_LAG and RUN_TO

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Message-ID: <20250212094307.GB19118@noisy.programming.kicks-ass.net>
Date: Wed, 12 Feb 2025 10:43:07 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Cristian Prundeanu <cpru@...zon.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>,
	Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>,
	Ali Saidi <alisaidi@...zon.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Geoff Blake <blakgeof@...zon.com>, Csaba Csoma <csabac@...zon.com>,
	Bjoern Doebel <doebel@...zon.com>,
	Gautham Shenoy <gautham.shenoy@....com>,
	Joseph Salisbury <joseph.salisbury@...cle.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-tip-commits@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 0/2] [tip: sched/core] sched: Disable PLACE_LAG and
 RUN_TO_PARITY and move them to sysctl

On Tue, Feb 11, 2025 at 11:41:13PM -0600, Cristian Prundeanu wrote:

> Your find also helps to point out that even when it works, SCHED_BATCH is 
> a more complex and error prone mitigation than just disabling PL and RTP. 
> The same reproducer setup that uses systemd to set SCHED_BATCH does show 
> improvement in 6.12, but not in 6.13+. There may not even be a single 
> approach that works well on both.
> 
> Conversely, setting NO_PLACE_LAG + NO_RUN_TO_PARITY is simply done at boot 
> time, and does not require further user effort. 

For your workload. It will wreck other workloads.

Yes, SCHED_BATCH might be more fiddly, but it allows for composition.
You can run multiple workloads together and they all behave.

Maybe the right thing here is to get mysql patched; so that it will
request BATCH itself for the threads that need it.