From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Nicolas Pitre <nicolas.pitre@linaro.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [PATCH 05/10] smp: Fast path check on IPI list
Date: Tue, 29 Jul 2014 23:55:37 +0200 [thread overview]
Message-ID: <20140729215536.GC14520@localhost.localdomain> (raw)
In-Reply-To: <20140729120739.GX3935@laptop>
On Tue, Jul 29, 2014 at 02:07:39PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 28, 2014 at 07:37:31PM +0200, Frederic Weisbecker wrote:
> > When we enqueue a remote irq work, we trigger the same IPI as those
> > raised by smp_call_function_*() family.
> >
> > So when we receive such IPI, we check both irq_work and smp_call_function
> > queues. Thus if we trigger a remote irq work, we'll likely find the
> > smp_call_function queue empty unless we collide with concurrent enqueuers
> > but the probability is low.
> >
> > Meanwhile, checking the smp_call_function queue can be costly because
> > we use llist_del_all() which relies on cmpxchg().
>
> xchg()
It's still costly though as it's an atomic read/write with full barrier. I'll
update the comment meanwhile.
next prev parent reply other threads:[~2014-07-29 21:55 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-28 17:37 [PATCH 00/10] nohz: Support sysidle (+ some more nohz kick cleanups) Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 01/10] smp: Introduce void kick_cpu_async() Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 02/10] nohz: Kick full dynticks timer targets with an empty IPI Frederic Weisbecker
2014-07-29 11:33 ` Peter Zijlstra
2014-07-29 21:53 ` Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 03/10] rcu: Kick full dynticks CPU on extended grace period with kick_cpu_async() Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 04/10] nohz: Appropriate timekeeper kick on sysidle break Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 05/10] smp: Fast path check on IPI list Frederic Weisbecker
2014-07-29 12:07 ` Peter Zijlstra
2014-07-29 21:54 ` Frederic Weisbecker
2014-07-29 21:55 ` Frederic Weisbecker [this message]
2014-07-28 17:37 ` [PATCH 06/10] nohz: Define meaningful symbol for nohz full timekeeper Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 07/10] nohz: Enforce timekeeping on CPU 0 Frederic Weisbecker
2014-07-29 12:12 ` Peter Zijlstra
2014-07-30 13:23 ` Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 08/10] nohz: Fetch timekeeping max deferment only for timekeeper Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 09/10] nohz: Switch nohz full timekeeper to dynticks idle on top of sysidle detection Frederic Weisbecker
2014-07-29 12:17 ` Peter Zijlstra
2014-07-29 22:04 ` Frederic Weisbecker
2014-07-28 17:37 ` [PATCH 10/10] nohz: Warn on illegal timekeeper switch in nohz full Frederic Weisbecker
-- strict thread matches above, loose matches on Subject: below --
2014-07-19 0:44 [RFC PATCH 00/10] nohz: Support sysidle (and some more cleanups) Frederic Weisbecker
2014-07-19 0:44 ` [PATCH 05/10] smp: Fast path check on IPI list Frederic Weisbecker
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