From: Andi Kleen <andi@firstfloor.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Andi Kleen" <andi@firstfloor.org>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"Ingo Molnar" <mingo@elte.hu>,
"Linux Kernel" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] tracing/function-return-tracer: Make the function return tracer lockless
Date: Thu, 13 Nov 2008 20:19:31 +0100 [thread overview]
Message-ID: <20081113191931.GB3810@one.firstfloor.org> (raw)
In-Reply-To: <alpine.DEB.1.10.0811131349090.31899@gandalf.stny.rr.com>
> barrier:
> __asm__ __volatile__("": : :"memory")
>
> local_add_return:
> asm volatile(_ASM_XADD "%0, %1;"
> : "+r" (i), "+m" (l->a.counter)
> : : "memory");
>
>
> Your argument was that barrier clobbers memory, but it looks like the
> local_add_return does the same.
That's a fair point. I'm not sure why the local_add_* has a memory
barrier at all, imho it shouldn't need it. I bet it's just
a hold over from the atomic code this was based one.
> I don't see any major gain in switching to local_add_return.
That's true with the current implementation. It would
be a good idea to consider dropping that explicit
barrier though, then it would be likely a slight win.
-Andi
--
ak@linux.intel.com
prev parent reply other threads:[~2008-11-13 19:10 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-11-12 21:47 [PATCH 1/2] tracing/function-return-tracer: Make the function return tracer lockless Frederic Weisbecker
2008-11-12 22:15 ` Ingo Molnar
2008-11-13 8:50 ` Frédéric Weisbecker
2008-11-13 8:55 ` Ingo Molnar
2008-11-13 9:16 ` Frédéric Weisbecker
2008-11-13 9:23 ` Ingo Molnar
2008-11-13 9:27 ` Frédéric Weisbecker
2008-11-13 9:40 ` Ingo Molnar
2008-11-13 12:36 ` Frédéric Weisbecker
2008-11-13 12:54 ` Ingo Molnar
2008-11-13 12:59 ` Peter Zijlstra
2008-11-13 13:02 ` Ingo Molnar
2008-11-13 17:26 ` Frédéric Weisbecker
2008-11-13 18:57 ` Ingo Molnar
2008-11-13 20:06 ` Frédéric Weisbecker
2008-11-13 14:53 ` Andi Kleen
2008-11-13 17:01 ` Frédéric Weisbecker
2008-11-13 17:12 ` Andi Kleen
2008-11-13 17:21 ` Steven Rostedt
2008-11-13 17:34 ` Andi Kleen
2008-11-13 17:32 ` Steven Rostedt
2008-11-13 17:46 ` Frédéric Weisbecker
2008-11-13 18:29 ` Andi Kleen
2008-11-13 18:35 ` Steven Rostedt
2008-11-13 18:55 ` Andi Kleen
2008-11-13 19:03 ` Steven Rostedt
2008-11-13 19:19 ` Andi Kleen [this message]
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