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

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Message-ID: <20241017091036.GT16066@noisy.programming.kicks-ass.net>
Date: Thu, 17 Oct 2024 11:10:36 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Cristian Prundeanu <cpru@...zon.com>
Cc: linux-tip-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	Bjoern Doebel <doebel@...zon.com>,
	Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>,
	Geoff Blake <blakgeof@...zon.com>, Ali Saidi <alisaidi@...zon.com>,
	Csaba Csoma <csabac@...zon.com>, gautham.shenoy@....com
Subject: Re: [PATCH 0/2] [tip: sched/core] sched: Disable PLACE_LAG and
 RUN_TO_PARITY and move them to sysctl

On Thu, Oct 17, 2024 at 12:19:58AM -0500, Cristian Prundeanu wrote:

> For example, running mysql+hammerdb results in a 12-17% throughput 

Gautham, is this a benchmark you're running?

> Testing combinations of available scheduler features showed that the 
> largest improvement (short of disabling all EEVDF features) came from 
> disabling both PLACE_LAG and RUN_TO_PARITY:

How does using SCHED_BATCH compare?

> While the long term approach is debugging and fixing the scheduler 
> behavior, algorithm changes to address performance issues of this nature 
> are specialized (and likely prolonged or open-ended) research. Until a 
> change is identified which fixes the performance degradation, in the 
> interest of a better out-of-the-box performance: (1) disable these 
> features by default, and (2) expose these values in sysctl instead of 
> debugfs, so they can be more easily persisted across reboots.

So disabling them by default will undoubtedly affect a ton of other
workloads. And sysctl is arguably more of an ABI than debugfs, which
doesn't really sound suitable for workaround.

And I don't see how adding a line to /etc/rc.local is harder than adding
a line to /etc/sysctl.conf