linux-kernel - Re: [RFC] arm: use built-in byte swap function

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Message-ID: <1363181704.32099.360.camel@i7.infradead.org>
Date:	Wed, 13 Mar 2013 13:35:05 +0000
From:	"Woodhouse, David" <david.woodhouse@...el.com>
To:	Kim Phillips <kim.phillips@...escale.com>
CC:	Nicolas Pitre <nico@...xnic.net>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Santos <daniel.santos@...ox.com>,
	David Rientjes <rientjes@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robherring2@...il.com>
Subject: Re: [RFC] arm: use built-in byte swap function

On Tue, 2013-02-19 at 20:31 -0600, Kim Phillips wrote:
> 
> > > imx_v6_v7_defconfig:        7672373         7667089         -5284
> > > lart_defconfig:     2941150         2941054         -96
> > > mxs_defconfig:      11091983        11095679        3696
> > 
> > The savings are good, with some impressive cases.  However the 
> > mxs_defconfig is completely the opposite and by far.  Any idea?
> 
> Unfortunately, I don't seem to be able to reproduce this anymore.
> Same linux-next, with three different compilers always produces
> smaller binaries:
> 
>    text    data     bss     dec     hex filename
> 5239363  280576 5569648 11089587         a936b3 linux-next-mxs-orig-gcc4.7/vmlinux
> 5239169  280556 5569648 11089373         a935dd linux-next-mxs-bswap-gcc4.7/vmlinux
> 
> 5262223  280592 5569648 11112463         a9900f linux-next-mxs-orig-gcc4.6.3/vmlinux
> 5261909  280584 5569648 11112141         a98ecd linux-next-mxs-bswap-gcc4.6.3/vmlinux
> 
> 5241379  280580 5569648 11091607         a93e97 linux-next-mxs-orig-gcc4.6ubuntu/vmlinux
> 5241189  280600 5569648 11091437         a93ded linux-next-mxs-bswap-gcc4.6ubuntu/vmlinux
> 
> So I've since made a more consistent cross-build environment, using
> cross tools from Linaro [1,2] instead of via Ubuntu [3].

Andrew Pinski has done some work on GCC to support further
optimisations: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55177

If you feel like building with the branch at
http://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=refs/heads/pinskia/bytewiseunop and seeing how that affects the results, that could be interesting.

-- 
                   Sent with MeeGo's ActiveSync support.

David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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