linux-kernel - 答复: [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: <73a9c4c3a3d94f06ab90129c4e4a9152@baidu.com>
Date:   Wed, 1 Sep 2021 07:19:30 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "mgorman@...e.de" <mgorman@...e.de>,
        "bristot@...hat.com" <bristot@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: 答复: [Resend][PATCH] sched/fair: micro-optimize pick_next_entity()



> -----邮件原件-----
> 发件人: Peter Zijlstra <peterz@...radead.org>
> 发送时间: 2021年8月31日 22:10
> 收件人: Li,Rongqing <lirongqing@...du.com>
> 抄送: 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
> 主题: 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?
> 
No 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.

True, next/last may be equal to skip  

-Li