On 05/15/2016 02:31 PM, Pavel Machek wrote:

Hi!

I'm playing some more with N900, this time I'd like to use it as a
alarm clock...

And now I realized I can not, because system performance is so
horrible with screen off that mpg123 + pulseaudio skips horribly. This
is without tweaking serial parameters, so CPU is definitely not going
into the idle/off modes.

Loading CPU fixes the issue (I used cat /dev/zero > /dev/null).

Hmm. And it seems to work better if I ssh in and launch mpg123
remotely. Weird.

Kernel 4.5-rc0. Will try on different ones.

Any ideas? Is there interface to tell kernel that better performance
is needed for a while?

pm_qos cpu_dma_latency? Drivers will have to be properly instrumented
with appropriate latency values -> this will control the depth in C
states that the system will attempt. NOTE: it is a dual edged sword,
bad configurations can result in none of the C-states being entered.


-- 
Regards,
Nishanth Menon