On Mon, Jul 28, 2014 at 1:00 PM, Joakim Hernberg <jbh@xxxxxxxxxx> wrote: > > I think this is due to running cyclictest as root, as it then > opens /dev/cpu_dma_latency and writes 0 into it. This has the > effect of disabling cpu powersaving. The cpu will no longer use P or C > states and runs full out. The result is that it finishes processing > the audio threads faster, thus lowering the DSP load shown in qjackctl > (which is a measure of how much of the available time until the > deadline did the audio processing take). The documentation is in > Documentation/power/pm_qos_interface.txt Note that it's not enough > to just write a value to it, the file needs to be kept open too, once > it's closed the cpu goes back to it's normal powersaving. > Thanks for this hint! I played around with adding processor.max_cstate=0 idle=halt to the boot parameters, which had the same effect as running cyclictest with /dev/cpu_dma_latency = 0.. I then removed this and had a poke around in the bios, and found that the main culprits for the xruns were C6 mode, and "AMD Power Now". Disabling these, and I now have an xrun-free experience with frames/period = 32/2 with pulseaudio/jack on my Scarlett 2i4, which is pretty amazing for a USB device IMO! There was also CPD mode and CState Pmin, which I disabled initially, but these don't seem to have any impact on xruns on my system. Cstate pmin seems to affect the reported DSP load - but otherwise doesn't affect xruns - so I think it's safe to keep on (and maybe is saving some power??). CPD mode doesn't seem to have any impact at all. James _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
