Subject: [linux-audio-dev] alsa latency statistics
From: dave willis (dubson_AT_dhammanet.net)
Date: Wed Oct 24 2001 - 04:54:30 EEST
i just finished testing several different patched and unpatched linux
kernels, and was surprised by the results: all basically the same.
alsa range = 33.4% to 33.8% 1.336 ms to 1.352 ms diff = 0.016 ms
oss-emu range = 91.6% to 91.9% 3.664 ms to 3.676 ms diff = 0.012 ms
as you can see, the differences are negligible and probably irrelevant if
more tested were done, and a standard 2.4.12 kernel is just as good as any
patched kernel.
one note: when i did a real-world test of latency by looping a signal
through my card and dividing the difference in time by 2 (because of input
and output latency), i got 3.675 ms latency using kernel 2.4.8-ll with oct
1 alsa-cvs, and that corresponds with the oss-emu latency for some reason
instead of the alsa latency. i don't know why, and i'll test this on
other kernels soon.
my system is an amd athlon 900 mhz running at 1006 mhz with redhat 7.1 and
an m-audio delta audiophile 2496 soundcard. i used alsa-cvs from october
20 and takashi iwai's modified version of latencytest0.42+alsa. the
kernels tested are 2.4.8-ll, 2.4.9-ll, 2.4.10-ll, 2.4.10-pe, 2.4.12,
2.4.12-ac2, 2.4.12-ac2-ll, 2.4.12-ac3, and 2.4.12-ac3-pe.
ll = low-latency
pe = pre-emptive
ac2 and ac3 are alan cox's patches
latencytest was ran as follows:
./latencytest -t alsa -d hw -q none 3 256
./latencytest -t oss -q none 3 256
-dave
details below:
-----------------------------------------------------------------------
sample rate = 48000
NUMBER of OVERRUNS = 0 PIXEL_PER_MS=112
fragment latency = 1.333333 ms buffer latency= 4.000 ms
fragment size=256 total buffer size=768
cpu_load= 80.0000% cpu latency = 1.066667 ms
with alsa, 100% of samples are within 1ms of buffer
used alsa-cvs from oct 20, oss = alsa's oss-emu
====================2.4.10-ll====================
output type = ALSA max latency=1.3 ms factor=33.4 % of buffer
output type = OSS max latency=3.7 ms factor=91.6 % of buffer
1MS factor=83.467993 2MS factor=99.937850
====================2.4.10-pe====================
output type = OSS max latency=3.7 ms factor=91.9 % of buffer
1MS factor=83.367698 2MS factor=99.965636
output type = ALSA max latency=1.3 ms factor=33.6 % of buffer
====================2.4.12-ac2-ll====================
output type = ALSA max latency=1.3 ms factor=33.7 % of buffer
output type = OSS max latency=3.7 ms factor=91.7 % of buffer
1MS factor=83.400810 2MS factor=99.932524
====================2.4.12-ac2====================
output type = ALSA max latency=1.3 ms factor=33.4 % of buffer
output type = OSS max latency=3.7 ms factor=91.7 % of buffer
1MS factor=83.372922 2MS factor=99.966067
====================2.4.12-ac3====================
output type = ALSA max latency=1.4 ms factor=33.8 % of buffer
output type = OSS max latency=3.7 ms factor=91.7 % of buffer
1MS factor=83.361392 2MS factor=99.971942
====================2.4.12-ac3-pe====================
output type = ALSA max latency=1.3 ms factor=33.5 % of buffer
output type = OSS max latency=3.7 ms factor=91.7 % of buffer
1MS factor=83.390216 2MS factor=99.943117
====================2.4.12====================
output type = ALSA max latency=1.3 ms factor=33.4 % of buffer
output type = OSS max latency=3.7 ms factor=91.7 % of buffer
1MS factor=83.372828 2MS factor=99.960506
====================2.4.8-ll====================
output type = ALSA max latency=1.3 ms factor=33.6 % of buffer
output type = OSS max latency=3.7 ms factor=91.6 % of buffer
1MS factor=83.402836 2MS factor=99.972199
====================2.4.9-ll====================
output type = ALSA max latency=1.3 ms factor=33.4 % of buffer
output type = OSS max latency=3.7 ms factor=91.7 % of buffer
1MS factor=83.385093 2MS factor=99.948240
This archive was generated by hypermail 2b28 : Wed Oct 24 2001 - 04:51:44 EEST