linux-kernel - Re: [PATCH 2/4] sched/fair: Small cleanup to sched_balance

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Message-ID: <20251114110510.GT278048@noisy.programming.kicks-ass.net>
Date: Fri, 14 Nov 2025 12:05:10 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, mingo@...hat.com,
	juri.lelli@...hat.com, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, linux-kernel@...r.kernel.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>
Subject: Re: [PATCH 2/4] sched/fair: Small cleanup to sched_balance_newidle()

On Fri, Nov 14, 2025 at 11:22:48AM +0100, Vincent Guittot wrote:

> sched_balance_update_blocked_averages() can be costly so we want to
> include it in the sd->max_idle_balance_cost so we skip newidle lb and
> update blocked load if avg_idle is shorter than doin the update and
> the newidle lb of the 1st level

Ah, fair enough.

> when sd is null we should still skip
> sched_balance_update_blocked_averages() is its cost is higher than
> avg_idle but it seems that we don't.

When !sd there is no balancing to be had.

Anyway, I'll keep the patch as is -- introducing an early exit for !sd
and I'll post a few more cleanups after this.