linux-kernel - Re: Attempted summary of suspend-blockers LKML thread

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Message-ID: <alpine.DEB.2.00.1008051715520.30632@asgard.lang.hm>
Date:	Thu, 5 Aug 2010 17:16:44 -0700 (PDT)
From:	david@...g.hm
To:	Brian Swetland <swetland@...gle.com>
cc:	paulmck@...ux.vnet.ibm.com,
	kevin granade <kevin.granade@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	pavel@....cz, florian@...kler.org, stern@...land.harvard.edu,
	peterz@...radead.org, tglx@...utronix.de, alan@...rguk.ukuu.org.uk
Subject: Re: Attempted summary of suspend-blockers LKML thread

On Thu, 5 Aug 2010, Brian Swetland wrote:

> On Thu, Aug 5, 2010 at 4:03 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
>>>> so what would wake a phone up from suspend where the phone should go back to
>>>> sleep in under a second?
>>>
>>> Here are some real-world examples from shipped android devices:
>>> - battery gauging happens every 10 minutes, need to wake long enough
>>> to chatter with the 1w interface and make sure the battery is not
>>> exploding
>>> - always on mail/im/calendar/etc sync often has network events that
>>> happen every 5-10 minutes which cause devices to briefly wake up and
>>> return to sleep
>>> - gps tracker app might wake every couple minutes or every n gps
>>> events to log location
>>> - low power audio subsystems can wake you up every 1-4 seconds (pcm)
>>> or 1-4 minutes (mp3) to fetch more data
>>
>> Interesting!
>>
>> So for an mp3 playback, does an Android suspend between data fetches?
>
> It can if the latency is long enough (which is why I point out low
> power audio which is usually high latency).  For low latency (system
> sounds, etc) 10-25ms between buffers it's not practical to fully
> suspend but we will go to the lowest power state in idle if possible.

the playback is able to continue even with all the clocks stopped? that 
surprises me. I would hav expected it to be able to sleep while playing 
audio, but not do a full suspend.

David Lang
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