cpu use flags
On Sun, 2008-04-20 at 13:39 -0400, Allan Gottlieb wrote:
> I have an intel core2 duo (currently in 32 bit mode x86).
> Is there any reason why I should not set the following use flags.
> mmx, sse, sse2, ssse3
> The last one would be a local flag for mplayer.
> proc/cpu indicates I have this functionality.
> flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm
> constant_tsc arch_perfmon pebs bts pni monitor ds_cpl vmx est tm2
> ssse3 cx16 xtpr lahf_lm
As a use flag, you should set all you can. They all enable the use of
optimized code and the code I've seen from this was clever enough to
choose the best if several were available.
Please don't confuse this with the CFLAGS in your make.conf, there you
should only choose the latest and this should be automatically applied
by march=nocona (one exception are newer Athlons, because
march=k8/athlon64/opteron/athlon-fx only activates SSE2 but not SSE3).
By the way: Does anyone know why mmx2 (or was it mmxext?) isn't listed
in cpuinfo for Core2 processors? Since it's a subset of SSE it should
really be there, right?