[pulseaudio-discuss] PulseAudio Painfully Slow

[Alexander E. Patrakov]

14.07.2014 22:11, Benny de von Ausfern wrote:
> Just to make sure, compiling libs (specially alsa-lib) with such
> CFLAGS might break a lot of things, since I'd be disabling some of my
> current flags, and that might catch other libs out of guard. This is my
> current CFLAGS
>
> CFLAGS="-march=core2"
> CFLAGS="${CFLAGS} -msse4"
> CFLAGS="${CFLAGS} -mcx16"
> CFLAGS="${CFLAGS} -msahf"
> CFLAGS="${CFLAGS} -O2"
> CFLAGS="${CFLAGS} -pipe"

Well, you may use your flags, just be sure to add -g3 -ggdb (they just 
add debug information), and FEATURES=splitdebug (so that the debug 
information is carefully put into a separate file instead of being 
discarded). It would also be interesting to compare whether your 
additional flags change anything, and I honestly don't know the answer.

OTOH, here is some evidence that some parts of PulseAudio react badly 
(in terms of performance) to non-standard CFLAGS. -O3 is 2x slower than 
-O2, due to hand-unrolled loops! I don't know how the -m* flags that you 
add will interact with such loops. Anything except mere -O2 is de-facto 
untested and unsupported in terms of performance (but should still be 
correct unless the compiler documentation says otherwise).

http://lists.freedesktop.org/archives/pulseaudio-discuss/2014-April/020533.html

-- 
Alexander E. Patrakov