xfce4-mixer-plugin generates about 10 wakeups per second on my system effectively shortening battery life. I am not sure if this is reproducible or what (if any) logs would be helpful but I am willing to provide necessary information.
Yeah, if you check "panel-plugin/plugin.c", line 507, it adds a timeout callback to be called every second: function is "mixer_timer_cb". Sorry, but this is by design because it polls for changes in the volume control values from time to time. If you want, comment out the line that says: mixer->timer = g_timeout_add (UPDATE_TIMEOUT, (GSourceFunc) mixer_timer_cb, mixer ); If you have and use ALSA ("./configure --with-sound=alsa"), that might even work without ill effects.
I mean replace by "mixer->timer = 0;"
and it should only wake up once per second... I also committed a small fix for 4.4 branch now that should at least make the panel settings dialog less demanding (that was refreshing the device list every 500ms or so sometimes). So it should be better now, and if you can, find the culprits which wake up the computer more often than once every second, and try the workaround I gave. You can find out which part it is by commenting out huge slabs of the xfce4-mixer plugin source code and see when it goes away. When you do this in a divide-and-conquer fashion, you don't need that many tries to find out. Make sure the culprit _is_ the mixer plugin before doing all that, though :)
Thanks! That actually sounds like an approach I could undertake once I have some spare time on my hands.