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

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Message-ID: <alpine.LFD.2.00.0901071529530.3057@localhost.localdomain>
Date:	Wed, 7 Jan 2009 15:32:11 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Gregory Haskins <ghaskins@...ell.com>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Peter Zijlstra <peterz@...radead.org>,
	paulmck@...ux.vnet.ibm.com, 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



On Wed, 7 Jan 2009, Steven Rostedt wrote:
> 
> What would be interesting is various benchmarks against all three.
> 
> 1) no mutex spinning.
> 2) get_task_struct() implementation.
> 3) spin_or_sched implementation.

One of the issues is that I cannot convince myself that (2) is even 
necessarily correct. At least not without having all cases happen inder 
the mutex spinlock - which they don't. Even with the original patch, the 
uncontended cases set and cleared the owner field outside the lock.

			Linus
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