On Jan 30, 11:58 am, William Stein <[email protected]> wrote:
> On Fri, Jan 30, 2009 at 11:50 AM, Carl Witty <[email protected]> wrote:
>
> > We have a problem finding and maintaining machines old enough to not
> > have SSE3, etc., so that we can reliably build Sage binaries that
> > don't rely on SSE3.
>
> > Evidently, vmware lets you mask CPUID results, to hide particular CPU
> > features from the guest:
> >http://pubs.vmware.com/vi3/bsa/wwhelp/wwhimpl/common/html/wwhelp.htm?...
>
> > Maybe we could use that as an easy way to be able to build no-SSE3
> > binaries.
>
> > I see two problems with the idea: 1) it's poorly documented; somebody
> > would have to figure out which bits to flip in the cpuid results.
>
> > 2) I'm guessing this doesn't actually disable the feature. If any
> > part of Sage does SSE3 detection by trying to run SSE3 code and seeing
> > if it crashes (instead of using the cpuid instruction), then the
> > technique would fail.
>
> This is certainly worth trying.
ATLAS does not use any detection code, but "just" compiles some
assembly to see if the feature is there or not, so it looks like this
won't work.
> It is a very high priority, IMHO, that we figure out how to build
> binaries on the
> vmware "farm" (which runs on boxen.math) that don't require these cpu
> instructions.
> I see two ways to do that:
>
> (1) What you suggest above using vmware, which might work. Note that
> vmware server, which I run on boxen.math, doesn't have the options you
> suggest modifying. However, I bet one can change them anyways through
> a text editor by directly editing the vm configuration.
>
> (2) Pass options to libraries that actually try to use these cpu
> flags -- e.g., ATLAS, GMP, etc. -- to tell them not to. Then use
> objdump (?) to detect whether we succeeded.
>
> I like (2) better if it can be made to work. Mabshoff claimed he
> could make it work in a few days, so maybe it is possible.
Yep, I have been playing around with this and I don't think it will be
too far into the future.
> -- William
Cheers,
Michael
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