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Re: alternatives
Hi,
Le Mon, 5 Nov 2007 11:31:13 +0000,
ninjaboy <n0b0dyn1nj4@xxxxxxxxx> a écrit :
> Yes, that makes sense, but why on AMD64 X2 is better rep insn than
> unrolled? In my userspace test case rep is slower than unrolled.
My knowledge of microprocessor internals is unfortunately too limited to
give a precise answer to your question.
However, you can see the code that sets X86_FEATURE_REP_GOOD at
http://lxr.free-electrons.com/source/arch/x86_64/kernel/setup.c#574.
The above comment says
« On C+ stepping K8 rep microcode works well for copy/memset »
You can read section 3.7.6 of the « Intel® 64 and IA-32 Architectures
Optimization Reference Manual » for more informations about using "rep"
for optimization. This manual is available at
http://www.intel.com/products/processor/manuals/index.htm.
Sincerly,
Thomas
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Thomas Petazzoni - thomas.petazzoni@xxxxxxxx
http://{thomas,sos,kos}.enix.org - http://www.toulibre.org
http://www.{livret,agenda}dulibre.org
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