linux-kernel - Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning

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Message-ID: <20090107212842.GD4597@elte.hu>
Date:	Wed, 7 Jan 2009 22:28:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 			/*
> 			 * Even if the access succeeded (likely case),
> 			 * the cpu field may no longer be valid. FIXME:
> 			 * this needs to validate that we can do a
> 			 * get_cpu() and that we have the percpu area.

s/get_cpu/cpu_rq ?

> 			 */
> 			if (cpu >= NR_CPUS)
> 				break;
> 
> 			if (!cpu_online(cpu))
> 				break;

Regarding the FIXME, this should be safe already - at least on x86 we set 
up all the possible-cpus-mask per CPU areas during bootup. So any CPU that 
is online, will have a percpu area. (even in the most racy case)

	Ingo
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