linux-kernel - Re: [PATCH 03/13] jump label v9: x86 support

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Message-ID: <20100610161339.GA20448@Krystal>
Date:	Thu, 10 Jun 2010 12:13:39 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de,
	rostedt@...dmis.org, andi@...stfloor.org, roland@...hat.com,
	rth@...hat.com, mhiramat@...hat.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, vgoyal@...hat.com,
	sam@...nborg.org
Subject: Re: [PATCH 03/13] jump label v9: x86 support

* Jason Baron (jbaron@...hat.com) wrote:
> On Thu, Jun 10, 2010 at 02:14:40PM +0200, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Wed, 2010-06-09 at 17:39 -0400, Jason Baron wrote:
> > > > +       select HAVE_ARCH_JUMP_LABEL if !CC_OPTIMIZE_FOR_SIZE
> > > 
> > > That deserves a comment somewhere, it basically makes OPTIMIZE_FOR_SIZE 
> > > useless...
> > 
> > Hm, we need more than a comment for that - distros enable CC_OPTIMIZE_FOR_SIZE 
> > all the time, for the massive kernel image (and hotpath cache footprint) 
> > savings. Is this fixable?
> > 
> > Thanks,
> > 
> > 	Ingo
> > 
> 
> When I tested 'jump label' with CC_OPTIMIZE_FOR_SIZE, I saw a small
> performance drop , b/c there is less block re-ordering happening.

Is this a performance drop compared to a jump-label-less kernel or
compared to -O2 kernel compiled with jump labels ? Or both ?

Mathieu


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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