From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
akpm@linux-foundation.org, josh@joshtriplett.org,
tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
dhowells@redhat.com, laijs@cn.fujitsu.com, dipankar@in.ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier
Date: Thu, 7 Jan 2010 08:39:23 -0800 [thread overview]
Message-ID: <20100107163923.GB6764@linux.vnet.ibm.com> (raw)
In-Reply-To: <1262853136.4049.81.camel@laptop>
On Thu, Jan 07, 2010 at 09:32:16AM +0100, Peter Zijlstra wrote:
> On Wed, 2010-01-06 at 21:02 -0800, Paul E. McKenney wrote:
> >
> > Beats the heck out of user-mode signal handlers!!! And it is hard
> > to imagine groveling through runqueues ever being a win, even on very
> > large systems. The only reasonable optimization I can imagine is to
> > turn this into a no-op for a single-threaded process, but there are
> > other ways to do that optimization.
> >
> > Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>
> Then imagine someone doing:
>
> while (1)
> sys_membarrier();
>
> on your multi node machine, see how happy you are then.
I guess in that situation, I would be feeling no pain. Or anything else
for that matter. :-/
So, good point!!! I stand un-Reviewed-By.
I could imagine throttling the requests, as well as batching them. If
any CPU does a sys_membarrier() after this CPU's sys_membarrier has
entered the kernel, then this CPU can simply return. A token-bucket
approach could throttle things nicely, but at some point it becomes
better to just do POSIX signals.
Thanx, Paul
next prev parent reply other threads:[~2010-01-07 16:39 UTC|newest]
Thread overview: 107+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-07 4:40 [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier Mathieu Desnoyers
2010-01-07 5:02 ` Paul E. McKenney
2010-01-07 5:39 ` Mathieu Desnoyers
2010-01-07 8:32 ` Peter Zijlstra
2010-01-07 16:39 ` Paul E. McKenney [this message]
2010-01-07 5:28 ` Josh Triplett
2010-01-07 6:04 ` Mathieu Desnoyers
2010-01-07 6:32 ` Josh Triplett
2010-01-07 17:45 ` Mathieu Desnoyers
2010-01-07 16:46 ` Paul E. McKenney
2010-01-07 5:40 ` Steven Rostedt
2010-01-07 6:19 ` Mathieu Desnoyers
2010-01-07 6:35 ` Josh Triplett
2010-01-07 8:44 ` Peter Zijlstra
2010-01-07 13:15 ` Steven Rostedt
2010-01-07 15:07 ` Mathieu Desnoyers
2010-01-07 16:52 ` Paul E. McKenney
2010-01-07 17:18 ` Peter Zijlstra
2010-01-07 17:31 ` Paul E. McKenney
2010-01-07 17:44 ` Mathieu Desnoyers
2010-01-07 17:55 ` Paul E. McKenney
2010-01-07 17:44 ` Steven Rostedt
2010-01-07 17:56 ` Paul E. McKenney
2010-01-07 18:04 ` Steven Rostedt
2010-01-07 18:40 ` Paul E. McKenney
2010-01-07 17:36 ` Mathieu Desnoyers
2010-01-07 14:27 ` Steven Rostedt
2010-01-07 15:10 ` Mathieu Desnoyers
2010-01-07 16:49 ` Paul E. McKenney
2010-01-07 17:00 ` Steven Rostedt
2010-01-07 8:27 ` Peter Zijlstra
2010-01-07 18:30 ` Oleg Nesterov
2010-01-07 18:39 ` Paul E. McKenney
2010-01-07 18:59 ` Steven Rostedt
2010-01-07 19:16 ` Paul E. McKenney
2010-01-07 19:40 ` Steven Rostedt
2010-01-07 20:58 ` Paul E. McKenney
2010-01-07 21:35 ` Steven Rostedt
2010-01-07 22:34 ` Paul E. McKenney
2010-01-08 22:28 ` Mathieu Desnoyers
2010-01-08 23:53 ` Mathieu Desnoyers
2010-01-09 0:20 ` Paul E. McKenney
2010-01-09 1:02 ` Mathieu Desnoyers
2010-01-09 1:21 ` Paul E. McKenney
2010-01-09 1:22 ` Paul E. McKenney
2010-01-09 2:38 ` Mathieu Desnoyers
2010-01-09 5:42 ` Paul E. McKenney
2010-01-09 19:20 ` Mathieu Desnoyers
2010-01-09 23:05 ` Steven Rostedt
2010-01-09 23:16 ` Steven Rostedt
2010-01-10 0:03 ` Paul E. McKenney
2010-01-10 0:41 ` Steven Rostedt
2010-01-10 1:14 ` Mathieu Desnoyers
2010-01-10 1:44 ` Mathieu Desnoyers
2010-01-10 2:12 ` Steven Rostedt
2010-01-10 5:25 ` Paul E. McKenney
2010-01-10 11:50 ` Steven Rostedt
2010-01-10 16:03 ` Mathieu Desnoyers
2010-01-10 16:21 ` Steven Rostedt
2010-01-10 17:10 ` Mathieu Desnoyers
2010-01-10 21:02 ` Steven Rostedt
2010-01-10 21:41 ` Mathieu Desnoyers
2010-01-11 1:21 ` Paul E. McKenney
2010-01-10 17:45 ` Paul E. McKenney
2010-01-10 18:24 ` Mathieu Desnoyers
2010-01-11 1:17 ` Paul E. McKenney
2010-01-11 4:25 ` Mathieu Desnoyers
2010-01-11 4:29 ` [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v3a) Mathieu Desnoyers
2010-01-11 17:27 ` Paul E. McKenney
2010-01-11 17:35 ` Mathieu Desnoyers
2010-01-11 17:50 ` Peter Zijlstra
2010-01-11 20:52 ` Mathieu Desnoyers
2010-01-11 21:19 ` Peter Zijlstra
2010-01-11 22:04 ` Mathieu Desnoyers
2010-01-11 22:20 ` Peter Zijlstra
2010-01-11 22:48 ` Paul E. McKenney
2010-01-11 22:48 ` Mathieu Desnoyers
2010-01-11 21:19 ` Peter Zijlstra
2010-01-11 21:31 ` Peter Zijlstra
2010-01-11 4:30 ` [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v3b) Mathieu Desnoyers
2010-01-11 22:43 ` Paul E. McKenney
2010-01-12 15:38 ` Mathieu Desnoyers
2010-01-12 16:27 ` Steven Rostedt
2010-01-12 16:38 ` Mathieu Desnoyers
2010-01-12 16:54 ` Paul E. McKenney
2010-01-12 18:12 ` Paul E. McKenney
2010-01-12 18:56 ` Mathieu Desnoyers
2010-01-13 0:23 ` Paul E. McKenney
2010-01-11 16:25 ` [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier Paul E. McKenney
2010-01-11 20:21 ` Mathieu Desnoyers
2010-01-11 21:48 ` Paul E. McKenney
2010-01-14 2:56 ` Lai Jiangshan
2010-01-14 5:13 ` Paul E. McKenney
2010-01-14 5:39 ` Mathieu Desnoyers
2010-01-10 5:18 ` Paul E. McKenney
2010-01-10 1:12 ` Mathieu Desnoyers
2010-01-10 5:19 ` Paul E. McKenney
2010-01-10 1:04 ` Mathieu Desnoyers
2010-01-10 1:01 ` Mathieu Desnoyers
2010-01-09 23:59 ` Paul E. McKenney
2010-01-10 1:11 ` Mathieu Desnoyers
2010-01-07 9:50 ` Andi Kleen
2010-01-07 15:12 ` Mathieu Desnoyers
2010-01-07 16:56 ` Paul E. McKenney
2010-01-07 11:04 ` David Howells
2010-01-07 15:15 ` Mathieu Desnoyers
2010-01-07 15:47 ` David Howells
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