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Date: Tue, 04 Feb 2003 07:50:59 -0800
From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Dave Jones <davej@suse.de>
cc: linux-kernel <linux-kernel@vger.kernel.org>,
       lse-tech <lse-tech@lists.sourceforge.net>
Subject: Re: [Lse-tech] gcc 2.95 vs 3.21 performance
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>  > People keep extolling the virtues of gcc 3.2 to me, which I'm
>  > reluctant to switch to, since it compiles so much slower. But
>  > it supposedly generates better code, so I thought I'd compile
>  > the kernel with both and compare the results. This is gcc 2.95
>  > and 3.2.1 from debian unstable on a 16-way NUMA-Q. The kernbench
>  > tests still use 2.95 for the compile-time stuff.
>  > 
>  > The results below leaves me distinctly unconvinced by the supposed 
>  > merits of modern gcc's. Not really better or worse, within experimental
>  > error. But much slower to compile things with.
> 
> What kernel was kernbench compiling ? The reason I'm asking is that
> 2.5s (and more recent 2.4.21pre's) will use -march flags for more
> aggressive optimisation on newer gcc's.
> If you want to compare apples to apples, make sure you choose
> something like i386 in the processor menu, and then it'll always
> use -march=i386 instead of getting fancy with things like -march=pentium4

Kernbench compiles 2.4.17, because I'm old, slow and lazy, and that
was what was around when I started doing this test ;-)

But the point is still the same ... even if it is doing more agressive
optimisation, it's not actually buying us anything (at least for the kernel)

M.

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