From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Clark Williams <williams@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [PATCH] sched: Do not release current rq lock on non contended double_lock_balance()
Date: Tue, 14 Jun 2016 13:52:45 -0400 [thread overview]
Message-ID: <20160614135245.65448383@grimm.local.home> (raw)
In-Reply-To: <20160614115820.GD30921@twins.programming.kicks-ass.net>
>
> > CPU 0 CPU 1
> > ----- -----
> > [ wake up ]
> > spin_lock(cpu1_rq->lock);
> > spin_lock(cpu1_rq->lock)
> > double_lock_balance()
> > [ release cpu1_rq->lock ]
> > spin_lock(cpu1_rq->lock)
> > [due to ticket, now acquires
> > cpu1_rq->lock ]
> >
> > [goes to push task]
> > double_lock_balance()
> > [ release cpu1_rq->lock ]
> > [ acquires lock ]
> > spin_lock(cpu2_rq->lock)
> > [ blocks as cpu2 is using it ]
> >
>
> Also, its not entirely clear this scenario helps illustrate how your
> change is better; because here the lock _is_ contended, so we'll fail
> the trylock, no?
Sorry, I should have been more specific that the double lock balance
was grabbing cpu2_rq (another rq lock), where there was no contention.
-- Steve
next prev parent reply other threads:[~2016-06-14 17:52 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-13 16:37 [PATCH] sched: Do not release current rq lock on non contended double_lock_balance() Steven Rostedt
2016-06-14 11:58 ` Peter Zijlstra
2016-06-14 17:52 ` Steven Rostedt [this message]
2016-06-14 18:02 ` Steven Rostedt
2016-06-14 19:42 ` Peter Zijlstra
2016-06-15 11:14 ` Peter Zijlstra
2016-06-15 16:13 ` Steven Rostedt
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