From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning
Date: Wed, 7 Jan 2009 23:33:17 +0100
Message-ID: <20090107223317.GB27629@elte.hu>
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Cc: Andi Kleen <andi@firstfloor.org>, Matthew Wilcox <matthew@wil.cx>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	paulmck@linux.vnet.ibm.com, Chris Mason <chris.mason@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nick Piggin <npiggin@suse.de>,
	Peter Morreale <pmorreale@novell.com>,
	Sven Dietrich <SDietrich@novell.com>
To: Gregory Haskins <ghaskins@novell.com>
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* Gregory Haskins <ghaskins@novell.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