Iwai, I checked the value of /sys/module/snd_hda_intel/parameters/power_save with less, it is set to 0 already.
On Wed, Feb 25, 2015 at 3:36 AM, Alexander E. Patrakov patrakov@gmail.com wrote:
25.02.2015 13:30, Jaroslav Kysela wrote:
Dne 25.2.2015 v 09:14 Alexander E. Patrakov napsal(a):
25.02.2015 03:46, Yomi Ogunwumi wrote:
Third. This is just a question. Is this : https://bugs.freedesktop.org/show_bug.cgi?id=86676 actually a pulseaudio bug, or is it an issue with alsa? I'm only asking since Raymond linked something that seemed to belong to the alsa project.
This is a bug both in ALSA and in PulseAudio.
The ALSA part (from the user viewpoint) is that the softvol plugin does not reprocess the already-submitted but buffered samples when the volume changes. But it can't, because that would require an additional thread for monitoring the software volume changes, and such thread does not exist.
The PulseAudio part of the bug is that it does not deactivate softvols, even though it can apply volume in software itself. In October 2014, in Dusseldorf, a general agreement has been reached on the following arguments:
- ALSA has no API to definitely distinguish softvols from other
controls.
- ALSA has the snd_ctl_elem_info_is_user() API function that tells
whether this is a userspace control.
- All softvols are userspace controls.
- There are other kinds of userspace controls, but they are rare.
- If a control is named PCM Playback Volume and is a userspace
control, then it's likely a softvol. Not bulletproof, but a good-enough heuristic.
- On finding a softvol, PulseAudio should set it to 100% (so that it
doesn't eat CPU) and don't touch from that point on.
But nobody has implemented this so far.
PulseAudio should open PCM with the SND_PCM_NO_SOFTVOL mode. In this case, the PCM device does not add the softvol plugin to the internal plugin chain. These mode flags was introduced a long time ago (discussed with Lennart) and I thought that PA uses it.
JaroslavWell, good to know, at least.
Well, that can be done, but the "don't attempt to control the softvol" part of the bug needs to be solved first. SND_PCM_NO_SOFTVOL by itself is not sufficient.
-- Alexander E. Patrakov