linux-kernel - Re: [RFC PATCH] sched/fair: Choose the CPU where short task is running during wake up

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Message-ID: <YyRhvEGS4ivPGf+z@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Sep 2022 13:45:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Tim Chen <tim.c.chen@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Aaron Lu <aaron.lu@...el.com>,
        Abel Wu <wuyun.abel@...edance.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Yicong Yang <yangyicong@...ilicon.com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched/fair: Choose the CPU where short task is
 running during wake up

On Fri, Sep 16, 2022 at 12:54:07AM +0800, Chen Yu wrote:
> And the rq lock bottleneck is composed of two paths(perf profile):
> 
> (path1):
> raw_spin_rq_lock_nested.constprop.0;
> try_to_wake_up;
> default_wake_function;
> autoremove_wake_function;
> __wake_up_common;
> __wake_up_common_lock;
> __wake_up_sync_key;
> pipe_write;
> new_sync_write;
> vfs_write;
> ksys_write;
> __x64_sys_write;
> do_syscall_64;
> entry_SYSCALL_64_after_hwframe;write

Can you please addr2line -i the raw_spin_rq_lock callsite so we know which is
the one causing grief?

Specifically; I'm worried about PSI, psi_ttwu_dequeue() can cause ttwu()
to take _2_ rq->lock, which absolutely blows for this case.