Again, some of the flags are being used wrong: Giuseppe please check the gcc docs, as some (most) flags are redundant with -02 and almost all are with -03. Things have changed radically in this area with the upgrade to 3.x
Bob Finch On Monday 24 March 2003 12:24 pm, Giuseppe Ghibò wrote: > w9ya wrote: > >As I understand the gcc docs, using both -march and -mcpu is odd. You > > should probably be running these tests with just -march or just -mcpu. > > There may be some other issues as well, but this is as good a place to > > start as any. > > > >Bob Finch > > > >On Wednesday 19 March 2003 03:12 pm, Austin wrote: > >>Here's a simple benchmark from Narfi. > >> > >>Athlon XP 2100. > >>Asus A7N8X motherboard (NForce2) > >>512 MB memory, PC2700 2-2-2 > >>Mandrake 9.0 > >> > >>############### > >># Compiling for athlon-xp > >>export CFLAGS="-march=athlon-xp -mcpu=athlon-xp -O3 -finline-limit=10000 > >>-ffast-math -fomit-frame-pointer"; export CXXFLAGS=$CFLAGS; make clean; > >>./configure --disable-assert --enable-cmov-extension > >> --enable-simd-accel; make > >> > >>############### > >># Compiling for i586 > >>export CFLAGS="-march=i586 -mcpu=i586 -O3"; export CXXFLAGS=$CFLAGS; make > >>clean; ./configure --disable-assert --enable-cmov-extension > >>--enable-simd-accel; make > >> > >>############### > >># Compiling for i586, no MMX used > >>export CFLAGS="-march=i586 -mcpu=i586 -O3"; export CXXFLAGS=$CFLAGS; make > >>clean; ./configure --disable-assert --disable-cmov-extension > >>--disable-simd-accel; make > >> > >>He ran these 3 versions of mpeg2enc one after the other, each 3 > >>times and I picked the best time for each version. The file encoded was > >>only 127MB so it fit into RAM. > >> > >>The best times of the 4 were: > >>athlon-xp: 12.16 > >>i586: 13.24 > >>i586, no mmx: 57.65 > >> > >>[ start quote ] > >> > >>In short: There are >>some<< packages which >>need to<< have mmx enabled. > >>These numbers should show that beyond any doubt! > >> > >>How we do it is a different question. > >> > >>My opinion is that going all the way and allowing the user to recompile > >> all packages is a potential support nightmare that Mandrake cannot risk > >> and that we should do the minimal: Only do this for a small number of > >> select packages where one can prove there is a significant benefit. > >> > >>If somebody recompiles OOo for athlon-xp and can show that the startup > >> time after a reboot can be cut by 50% when compared to the i586 version, > >> I am all for it. Otherwise, I don't think it's worth the risk. > >> > >>Narfi > >> > >>[ end quote ] > >> > >>So you see, 4.4 times faster by enabling MMX, and 4.7 times faster by > >> also enabling fast-math athlon XP. Thus it looks like your average app > >> will see very little increase in performance by recompiling for XP or P4 > >> or whatever, but as it stands now, our video apps are almost unuseably > >> slow. > >> > >>Austin > > I get a 3.5 times faster on PIII. Honestly I never found yet a package > that will increase > performance of even 10% just changing the compiler flags. Generally > the best achievement from current %optflags to best one or even forcing > -ffast-math and/or -fpmath=sse -march=..., is negligible, from 2-3% to > 5%. Effectively in package > mjpegtools this performance increase is severe tue to mmx usage; you can > try, compiling this one: > > http://people.mandrakesoft.com/~ghibo/mjpegtools-1.6.1-2mdk.src.rpm > > using > > rpm -ba --with mmx mjpegtools.spec > > note how the performance increase is almost ZERO removing -ffast-math > from CFLAGS, and or > using: > > --target i686-mandrake-linux > > as rpm building option. > > Maybe it's worthwhile to provide a separated .i686 package for that. I > wonder if there > are other packages like this giving more that 50% in performance > increasing just changing > some compiler option or compiler flag. > > Bye. > Giuseppe.
