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

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Date:	Wed, 7 Jan 2009 23:33:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Matthew Wilcox <matthew@....cx>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	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


* Gregory Haskins <ghaskins@...ell.com> wrote:

> Can I ask a simple question in light of all this discussion?
> 
> "Is get_task_struct() really that bad?"

it dirties a cacheline and it also involves atomics.

Also, it's a small design cleanliness issue to me: get_task_struct() 
impacts the lifetime of an object - and if a locking primitive has 
side-effects on object lifetimes that's never nice.

	Ingo

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