linux-kernel - Re: [PATCH] sched: optimize __cond_resched

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Message-ID: <YcHCEm/6AL0DQrv7@hirez.programming.kicks-ass.net>
Date:   Tue, 21 Dec 2021 13:01:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     xuhaifeng <xuhaifeng@...o.com>
Cc:     mingo@...hat.com, juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] sched: optimize __cond_resched_lock()

On Tue, Dec 21, 2021 at 11:09:00AM +0100, Peter Zijlstra wrote:
> On Tue, Dec 21, 2021 at 09:52:28AM +0100, Peter Zijlstra wrote:
> > On Tue, Dec 21, 2021 at 03:23:16PM +0800, xuhaifeng wrote:
> > > if the kernel is preemptible(CONFIG_PREEMPTION=y), schedule()may be
> > > called twice, once via spin_unlock, once via preempt_schedule_common.
> > > 
> > > we can add one conditional, check TIF_NEED_RESCHED flag again,
> > > to avoid this.
> > 
> > You can also make it more similar to __cond_resched() instead of making
> > it more different.
> 
> Bah, sorry, had to wake up first :/
> 
> cond_resched_lock still needs to exist for PREEMPT because locks won't
> magically release themselves.
> 
> Still don't much like the patch though, how's this work for you?
> 
> That's arguably the right thing to do work PREEMPT_DYNAMIC too.

Duh, those would need cond_resched() proper, clearly I should just give
up and call it a holiday already..