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List:       kde-kimageshop
Subject:    Re: cpu detection
From:       Boudewijn Rempt <boud () valdyas ! org>
Date:       2012-10-29 8:50:33
Message-ID: alpine.LNX.2.00.1210290947270.26686 () calcifer ! valdyas ! org
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On Mon, 29 Oct 2012, Dmitry Kazakov wrote:

> On Mon, Oct 29, 2012 at 12:28 PM, Boudewijn Rempt <boud@valdyas.org> wrote:
> I'm not sure whether there's already something suitably cross-platform in solid, \
> but Rami Radi from Intel pointed me at \
> http://libcpuid.sourceforge.net/documentation.html -- we could use that to make \
> sure that binaries compiled with avx support don't crash on non-avx systems but use \
> the fallback. 
> 
> As far as I know Vc does its own check for the presence of a particular instruction \
> set on the runtime, so it won't crash at least. But as reported by Sven its own \
> fallbacks are slower than our integer implementation of the routines.

I came across something yesterday that I cannot find that said that, yes, 
if you use a binary compiled for avx on a non-avx system, as soon as the 
instructions are executed you'll get a crash.

> I had an idea to perform a short set of benchmarks on a Krita start (or on first \
> start?) instead of inspecting a CPU and choose the most suitable implementation, \
> basing of these values. I guess, it should be the best solution for the problem, \
> since we can't test the performance of Krita on all the possible CPUs.

That's an interesting idea.

> But the optimized compilation of the Vc might be really a problem for usual users. \
> We (and distributions) need to think about it well.

I've asked on the packager mailing list for input on that problem

Boudewijn
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