On Mon, 2008-08-04 at 10:24 +0900, Charles Plessy wrote: > Le Sun, Aug 03, 2008 at 05:32:26PM +0200, Michel Dänzer a écrit : > > On Sun, 2008-08-03 at 11:53 +0900, Charles Plessy wrote: > > > > > > The result is that on some particular types of computations, the G5 > > > performs extremely bad: something like twice slower as an old 1.5 Ghz > > > Celeron machine. For some other tests, the performances of the > > > processors scale with the frequency. > > > > Most likely, the x86 binaries tend to have optimizations for SSE/MMX > > whereas the powerpc binaries tend not to have VMX/Altivec optimizations. > > Hi Michel, > > Is it somthing that can be turned on, or does it require modifications > to the sources? Quoting a GCC webpage: > > "The interface is made available by including <altivec.h> and using > -maltivec and -mabi=altivec." > > http://gcc.gnu.org/onlinedocs/gcc/PowerPC-AltiVec-Built_002din-Functions.html
These flags are prerequisites for allowing the resulting binaries to contain Altivec code at all, but on their own they don't cause any such code to be generated (except maybe for some simple cases like memory copies). Current versions of GCC can automatically vectorize some code with -ftree-vectorize, but the results probably still can't compete with hand-optimized code. Also note that these flags will make the resulting binaries unusable on systems without Altivec support. > The case in which I saw the biggest difference if for the building of > the 'exonerate' package: it took 9 h on a bi-G5 2GHz, compared to 1 h 30 > on the i386 buildd, 30 min on the alpha buildd, and > 30 h on the MIPS > buildds. Not sure that's directly related... I suspect this could be rather due to different amounts of RAM. (Even so though, it seems weird the alpha buildd could be so fast...) Case in point: http://buildd.debian.org/fetch.cgi?pkg=exonerate;ver=1.4.0-1;arch=powerpc;stamp=1194440576 says 04:17:30, and voltaire is an old dual G4 500 MHz... Though interestingly, https://db.debian.org/machines.cgi?host=voltaire also says it only has 320 MB of RAM... BTW, did you pass -j2 to dpkg-buildpackage and/or set DEB_BUILD_OPTIONS="parallel=2" to try and make the build use both cores? > I am starting to wonder if some of the binaries we ship in Debian Med > for bioinformatic computation are useful on PowerPC. It must obviously > depend on what kind of calculation they are doing. Is there a way to > guess other than by benchmark? Not sure, but I suspect not - in general, the only way to be sure if a given setup is suitable for XYZ is to try XYZ on the given setup. :) -- Earthling Michel Dänzer | http://tungstengraphics.com Libre software enthusiast | Debian, X and DRI developer -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
