linux-kernel - Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock

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Date:   Wed, 5 May 2021 09:20:38 -0700
From:   Don Hiatt <dhiatt@...italocean.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Don <joshdon@...gle.com>, Aubrey Li <aubrey.intel@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        "Hyser,Chris" <chris.hyser@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...e.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock

On Tue, May 4, 2021 at 12:38 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Apr 29, 2021 at 01:39:54PM -0700, Josh Don wrote:
>
> > > > +void double_rq_lock(struct rq *rq1, struct rq *rq2)
> > > > +{
> > > > +       lockdep_assert_irqs_disabled();
> > > > +
> > > > +       if (rq1->cpu > rq2->cpu)
> > >
> > > It's still a bit hard for me to digest this function, I guess using (rq->cpu)
> > > can't guarantee the sequence of locking when coresched is enabled.
> > >
> > > - cpu1 and cpu7 shares lockA
> > > - cpu2 and cpu8 shares lockB
> > >
> > > double_rq_lock(1,8) leads to lock(A) and lock(B)
> > > double_rq_lock(7,2) leads to lock(B) and lock(A)
>
> Good one!

Hi Peter,

I've been running the same set-cookie tests on your latest repo for
the last 24 hours and haven't had a single lockup. Thank you very
much!

don