linux-kernel - Re: [Resend][PATCH] sched/fair: micro-optimize pick_next

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: <YS44IzVARx2ZaEUo@hirez.programming.kicks-ass.net>
Date:   Tue, 31 Aug 2021 16:09:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Li RongQing <lirongqing@...du.com>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [Resend][PATCH] sched/fair: micro-optimize pick_next_entity()

On Wed, Aug 25, 2021 at 02:27:49PM +0800, Li RongQing wrote:
> Only check the skip buddy when next buddy and last buddy
> are not picked up, this can save the cycles of checking
> the skip buddy and computation of the second buddy, when
> next and last buddy will be picked up
> for example, yield_to_task_fair() set both next and skip
> buddy

Is that actually measurable?

But looking at it, should we not, instead, move the whole ->skip thing to
the bottom, so we unconditionally check it vs the result of
->next/->last ?

Imagine ->next == ->skip, then we want to avoid running it and not have
->next win.