答复: [Resend][PATCH] sched/fair: micro-optimize pick_next_entity()

["Li,Rongqing" <lirongqing@baidu.com>]

> -----邮件原件-----
> 发件人: Peter Zijlstra <peterz@infradead.org>
> 发送时间: 2021年8月31日 22:10
> 收件人: Li,Rongqing <lirongqing@baidu.com>
> 抄送: mingo@redhat.com; juri.lelli@redhat.com; vincent.guittot@linaro.org;
> dietmar.eggemann@arm.com; rostedt@goodmis.org; bsegall@google.com;
> mgorman@suse.de; bristot@redhat.com; linux-kernel@vger.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?
> 
> 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.

skip means this task is running on cpu, next is the blocked task and will be running.

I donot know how they can be same.

-Li