linux-kernel - Re: [PATCH][RFC]: mutex: adaptive spin

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Message-ID: <alpine.LFD.2.00.0901060857360.3057@localhost.localdomain>
Date:	Tue, 6 Jan 2009 08:59:52 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH][RFC]: mutex: adaptive spin



On Tue, 6 Jan 2009, Ingo Molnar wrote:
> 
> So instead of the BUG_ON() we could emit a WARN_ONCE() perhaps, plus not 
> do any spinning and just block - resulting in an uninterruptible task 
> (that the user will probably notice) and a scary message in the syslog? 
> [all in the slowpath]

Sure. You could put it in the adaptive function thing, with something like

	if (WARN_ONCE(waiter == owner))
		return 1;

which should fall back on the old behavior and do the one-time warning.

			Linus
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