[Paul Davis] >On Fri, 2008-02-01 at 08:14 +0100, Yann Orlarey wrote: > >> The minimal combination to activate FTZ mode seems to be : >> >> "-O3 -march=native -mfpmath=sse -ffast-math" >> >> when you are on a sse capable cpu. Here it works, you don't have >> denormals any more :-). > >Ardour takes manual control of FTZ and DAZ flags, and also offers DC >offsets (adding a very very tiny value to every sample) as ways to >control denormals. Our experience (or our users' experience) has been >that FTZ is better than DAZ, but that neither reduces denormal effects >as much as a DC offset. It is still possible to see denormal-induced >performance slowdowns even when FTZ is in effect, although the magnitude >is reduced.
On this Core2 (6600) chip, this: #ifdef __SSE3__ _MM_SET_DENORMALS_ZERO_MODE (_MM_DENORMALS_ZERO_ON); #endif #ifdef __SSE__ _MM_SET_FLUSH_ZERO_MODE (_MM_FLUSH_ZERO_ON); #endif along with -mfpmath=sse -msse -msse3 reliably eliminates denormals completely. DSP code runs at full speed with no more need for DC, noise, Nyquist or other signal injection. Flush-to-zero alone did not bring a palpable improvement when I evaluated the different options. On this chip that is, of course. Cheers, Tim _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev
