linux-kernel - Re: [PATCH 0/5] [GIT PULL] ring-buffer: optimize to 17% performance increase

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Date:	Tue, 12 May 2009 16:33:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 0/5] [GIT PULL] ring-buffer: optimize to 17%
	performance increase


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Tue, 12 May 2009, Steven Rostedt wrote:
> > > 
> > > It's also interesting to see that text size went down when speed 
> > > went up. I'm wondering how these compiler options:
> > 
> > But that was not always the case. The biggest boost in performance of the 
> > series (the last patch) also increased the size.
> > 
> > > 
> > >   CONFIG_CC_OPTIMIZE_FOR_SIZE=y
> > >   CONFIG_OPTIMIZE_INLINING=y
> > 
> > Note, my test runs had both the above configure options disabled.
> > I'll run it again and see how they affect the results:
> 
> Here's the results:
> 
> size=n inline=n  270 
> size=n inline=y  290
> size=y inline=n  315
> size=y inline=y  372 (ouch!)
> 
> Thus it seems to keep both optimizations off is best for performance.

ok. Maybe newer gcc does better with size=y. optimize-inline=n is 
not a surprise - this is in essence a micro-benchmark where inlining 
helps - and gcc's inliner isnt too fantastic either.

	Ingo
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