linux-kernel - Re: [RFC PATCH 0/8] sched/fair: Propagate load balancing stats up the sched domain hierarchy

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Message-ID: <20250317172536.GF6888@noisy.programming.kicks-ass.net>
Date: Mon, 17 Mar 2025 18:25:36 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Chen Yu <yu.c.chen@...el.com>, linux-kernel@...r.kernel.org,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	David Vernet <void@...ifault.com>,
	"Gautham R. Shenoy" <gautham.shenoy@....com>,
	Swapnil Sapkal <swapnil.sapkal@....com>,
	Shrikanth Hegde <sshegde@...ux.ibm.com>
Subject: Re: [RFC PATCH 0/8] sched/fair: Propagate load balancing stats up
 the sched domain hierarchy

On Thu, Mar 13, 2025 at 09:37:38AM +0000, K Prateek Nayak wrote:
> tl;dr
> 
> This prototype is currently limited in the sense that it can only reuse
> statistics for busy load balancing. Reusing stats for newidle load
> balancing specifically ran into issues elaborated below.

Right, it makes sense for busy load balance, newidle I think:

> David had proposed SHARED_RUNQ [4] to improve on the shortcomings of
> newidle balance for Meta's production workloads.

we need to look at this again. Something around the EEVDF merge made the
thing unhappy -- if we figure out what and fix it, I think this makes
more sense than trying to optimize the current scheme for newidle.

newidle really is about getting *any* work fast, which is a totally
different game than the regular busy balancing.

Anyway, I'll try and have a look through the patches.