linux-kernel - Re: [PATCH 1/1] sched/fair: improve yield

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YQALDHw7Cr+vbeqN@hirez.programming.kicks-ass.net>
Date:   Tue, 27 Jul 2021 15:33:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>, bristot@...hat.com,
        bsegall@...gle.com, dietmar.eggemann@....com, joshdon@...gle.com,
        juri.lelli@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux@...musvillemoes.dk, mgorman@...e.de, mingo@...nel.org,
        rostedt@...dmis.org, valentin.schneider@....com,
        vincent.guittot@...aro.org
Subject: Re: [PATCH 1/1] sched/fair: improve yield_to vs fairness

On Fri, Jul 23, 2021 at 10:35:23AM +0100, Mel Gorman wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 44c452072a1b..ddc0212d520f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4522,7 +4522,8 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
>  			se = second;
>  	}
>  
> -	if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) {
> +	if (cfs_rq->next &&
> +	    (cfs_rq->skip == left || wakeup_preempt_entity(cfs_rq->next, left) < 1)) {
>  		/*
>  		 * Someone really wants this to run. If it's not unfair, run it.
>  		 */

With a little more context this function reads like:

	se = left;

	if (cfs_rq->skip && cfs_rq->skip == se) {
		...
+		if (cfs_rq->next && (cfs_rq->skip == left || ...))

If '...' doesn't change @left (afaict it doesn't), then your change (+)
is equivalent to '&& true', or am I reading things wrong?