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
