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

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Message-Id: <1231370064.3470.516.camel@hermosa.site>
Date:	Wed, 07 Jan 2009 23:14:24 +0000
From:	"Peter W. Morreale" <pmorreale@...ell.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Gregory Haskins <ghaskins@...ell.com>,
	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>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning

On Wed, 2009-01-07 at 15:51 -0700, Peter W. Morreale wrote:
> On Wed, 2009-01-07 at 23:33 +0100, Ingo Molnar wrote:
> > * 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.
> > 
> 
> True, but it's for one iteration * NR_CPUS, max.
> 
> Best,
> -PWM

Never mind.  Bogus argument.  

That's why we have you Big Guns out there... - To keep us rif-raf in
line... 

:-)

Best,
-PWM

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