Am 17.08.2012 10:58, schrieb Jorge Almeida: > I'm in need of some expert advise about CFLAGS. I'm going to install > Gentoo in two systems, an Atom 330 and a P4 prescott. Since compiling > lots of stuff in an Atom is less than joyful, I intend to do almost > all compilation on the prescott and produce binary packages to use on > the Atom. So, something like > CFLAGS="-march=native ..." is out. I know I could set > CFLAGS="-march=i686 -O2 -pipe -fomit-frame-pointer", but I would like > to extract a bit more juice from the hw, while still keeping stable > systems. So, I thought of setting CFLAGS for both systems as > -march=i686, plus the flags that are pulled by -march=native in both > systems, plus some other flags: > [...] > > This is what is pulled by -march=native, using gcc -march=native -E -v > - </dev/null 2>&1 | grep cc1 > > Prescott: > -march=prescott -mno-cx16 -mno-sahf -mno-movbe -mno-aes -mno-pclmul > -mno-popcnt -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi > -mno-bmi2 -mno-tbm -mno-avx -mno-avx2 -mno-sse4.2 -mno-sse4.1 > -mno-lzcnt -mno-rdrnd -mno-f16c -mno-fsgsbase --param l1-cache-size=16 > --param l1-cache-line-size=64 --param l2-cache-size=1024 > -mtune=prescott > > Atom: > -march=atom -mcx16 -msahf -mmovbe -mno-aes -mno-pclmul -mno-popcnt > -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-bmi2 > -mno-tbm -mno-avx -mno-avx2 -mno-sse4.2 -mno-sse4.1 -mno-lzcnt > -mno-rdrnd -mno-f16c -mno-fsgsbase --param l1-cache-size=24 --param > l1-cache-line-size=64 --param l2-cache-size=512 -mtune=atom > [...] > > Some questions: > > 1) Is this strategy right? If so, any other flags to add? (or any > flags to remove from the list?) > > 2) The --param flags are the ones of the computer that will do the > compiling. I'm guessing the produced binaries are compatible with cpu > with different --param flags. Is this right? > > TIA > > Jorge Almeida >
1) Yes. But as you can see, -march=prescott is basically a subset of atom. In fact, before there was a -march=atom option, prescott was the best flag for atoms. I think you can avoid some hassle by simply enabling "-march=prescott --param l1-cache-line-size=64 --param l2-cache-size=512". 2) Yes, the param flags do not affect compatibility. Using the lower value will probably be better but this is just an educated guess. Regards, Florian Philipp
signature.asc
Description: OpenPGP digital signature
