Am 28.12.2010 00:26, schrieb Nick Copeland: >> > Now PA does use >> > quite a lot of CPU on the N900 - the +/-2% it requires on my laptop >> > translates into about 25% on Maemo, this really is quite an overhead and >> > as far as I can tell it does not change with sampling rate (I get the >> > same overhead with 48kHz as with 44.1kHz although I will retest that). >> >> btw, one thing to watch out when doing measurements is the CPU >> frequency... N900 uses very aggressive cpufreq and even with heavy audio >> processing, the CPU is not necessarily running at full speed (so even if >> top shows 25%, that doesn't necessarily mean that only 75% processing >> capacity is left for apps). But this is really only a problem when making >> measurements (the cpufreq is boosted automatically when needed). > > The CPU load for pulseaudio does not appear to change much with sampling > rate, taking 24kHz, 48kHz gives a very similar profile but you mention a bug > report that notes that fact anyway. Bristol does have a very different > footprint > depending on sampling rate and filter selection. > > The code will attempt to set the CPU freq to 600MHz when it starts, it does > not necessarily need these cycles but it helps to reduce underruns. Pulse > now rolls along at about 8% to 10% CPU for any rates I have tried and bristol > will take about 8% at 24kHz and double that (17%) for 48kHz. > >> There should be no resampling happening (if you use 48kHz), so it >> should not be that. But if src is used in your case, N900 uses speex src >> (speex-fixed-2) optimized for arm NEON (see Siarhei's comment in bug for >> info and links: >> https://test.maemo.org/testzilla/show_bug.cgi?id=5794#c10 ). > > This refers to the same data as above, ie, the resampling algorithm is not > where the CPU cycles are being spent. The report discusses the same results > as above but comparing 44.1kHz to 48kHz. > >> Don't take this too seriously, but I've personally found it a bit >> suprising how much negative feedback there has been about the audio mixer >> CPU cycles. In phones (versus desktop/laptops), some processing is needed >> as audio quality (especially for voice calls) is a closely followed aspect >> (it is benchmarked by various parties and various organizations have >> detailed requirements concerning it). > > It is sometimes difficult to understand the added value of a given process. > My first reply noted the fact that a complete synth voice with osc/mix/fil/env > and all its internal processing overhead had a lower footprint than the audio > daemon. It is easy to fall into 'Sendmail Syndrome' implying that the process > takes a lot of time, effort (in sendmails case configuration as well) whilst > not evidently bringing much to the table.
Sorry for the very late reply. One thing to mention is that the CPU load for pulse is going wown quite a bit when plugin headphones. Otherwise it runs some extra processing needed to accomodate the speakers. Stefan _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
