linux-kernel - Re: Can not play audio with screen off

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Date:	Mon, 16 May 2016 09:22:46 -0500
From:	Nishanth Menon <nm@...com>
To:	Pavel Machek <pavel@....cz>, <pali.rohar@...il.com>,
	<sre@...nel.org>, kernel list <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>, <tony@...mide.com>,
	<khilman@...nel.org>, <aaro.koskinen@....fi>,
	<ivo.g.dimitrov.75@...il.com>, <patrikbachan@...il.com>,
	<serge@...lyn.com>
Subject: Re: Can not play audio with screen off

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