On Mon, Dec 8, 2008 at 12:53 PM, William Stein <[EMAIL PROTECTED]> wrote: > On Mon, Dec 8, 2008 at 12:51 PM, Clint Whaley <[EMAIL PROTECTED]> wrote: >> William, >> >>>Is there an easy way to build an ATLAS but without it using any sse >>>(or other "modern") optimizations? >>> >>>See the little discussion below. The main issue is that I want to be >>>able to build a binary on a Xeon box that will work on an old Athlon >>>box. I have a 32-bit Linux OS installed on the Xeon box. >> >> First off, this is a *bad* idea (unfortunately, one everyone seems to want >> to do :); A Xeon-tuned library will be very poorly optimized for an Athlon. > > There are very very few users who will use this version of Sage. In > fact, they are *only* people whose current performance is 0, because > they can't build/use Sage at all. So I guess terrible is a lot > faster than 0. :-) > >> However, if you insist on crippling my performance, it may be possible: >> you will need to add the flags telling gcc not to add any SSE instructions >> to all compiler flags, using the configure command as described: >> >> http://math-atlas.sourceforge.net/atlas_install/atlas_install.html#SECTION00042000000000000000 >> >> Then, passing -V 0 to configure will tell ATLAS to not use any vector >> extensions itself. >> >> Like I say, this might work, but it will be a terrible Athlon library. You >> will probably drop your performance by a third or half by doing this . . . > > I think the only other option for us would be to use GSL's cblas, which would > drop performance by at least a factor of 10, and be a major pain to > maintain too. > > Thanks! > > -- William >
Clint's response (he's the developer of Atlas): I think the only other option for us would be to use GSL's cblas, which would >drop performance by at least a factor of 10, and be a major pain to >maintain too. I guess the thing is that you have to build a library, but you don't have access to the machine? If that is so, I would also override ATLAS's architecture detection, so that you can use the appropriate architectural defaults (I give you this info mainly to for future reference, since ATLAS currently has no class Athlon arch defaults). If you built it on a modern Athlon-64, you could turn off only SSE, and leave on 3DNow!, for instance, which would give you prefetch. In any installed ATLAS bin directory, issue : make xprint_enums ; ./xprint_enums This give you a list of the integers that are associated with various ATLAS enums, so that you can override them on the configure line. So, to make ATLAS believe my Athlon-64 is really a classic Athlon, I would probably pass something like: -b 32 -A 19 -V 16 -Fa al '-mfpmath=387 -mnosse -mno-sse2 -mno-sse3' Passing -V 0 is safer, since then ATLAS won't add 3dnow prefetch inst either (3dnow will cause problems if run on an intel). I would probably also force the L1 detection to the correct value. Unfortunately, I no longer have access to a classic athlon myself, and so the present package doesn't have arch defs for Athlon. This is unfortunate, since there is a special kernel used only on the classic athlon that gets 92% of peak, where the best normal code gets 72% (an assembly optimization for the weak frontend is required on this platform). Cheers, --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
