Subject: Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning
From: "Peter W. Morreale" <pmorreale@novell.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Gregory Haskins <ghaskins@novell.com>, 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>,
       Sven Dietrich <SDietrich@novell.com>
In-Reply-To: <20090107223317.GB27629@elte.hu>
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Organization: Linux Solutions Group
Date: Wed, 07 Jan 2009 22:51:05 +0000
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On Wed, 2009-01-07 at 23:33 +0100, Ingo Molnar wrote:
> * 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.
> 

True, but it's for one iteration * NR_CPUS, max.

Best,
-PWM


> 	Ingo
> 

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