Re: Building with -msse
On Sat, Apr 26, 2008 at 07:05:17PM -0700, Russ Allbery wrote:
> gnubg supports optionally building with SSE support for increased speed in
> the analytical engine. I have to date kept this disabled to not generate
> binaries that might not run on all otherwise-supported Debian systems.
>
> However, a user mentioned that he thinks all chips that fall into the
> amd64 architecture have SSE and hence adding -msse would be safe for the
> amd64 build. Is that correct?
There is no need to enable -msse on amd64. It has always been on by
default.
> And in general are there any guidelines
> about things like this? I assume that using -msse for the i386 build is
> still out since we still support 486 chips.
If you want to have different optimizations depending on the cpu,
there are a two options I know of:
- When you hace shared libraries you can put them in directories like
/usr/lib/i686/sse/. The dynamic linker whould pick it up for
you in that case. (I have no idea if it looks at i686/sse or not,
but it looks at various other dirs, I can't find documentation for it.)
- Use runtime detection of the cpu and select the best option yourself.
> (I don't think the performance gain warrants the complexity of building
> two binaries, although it is noticable.)
It all depends if you think the performance gain is worth it.
Kurt
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