Re: Attempted summary of suspend-blockers LKML thread

From: david
Date: Wed Aug 04 2010 - 15:17:35 EST

On Wed, 4 Aug 2010, Matthew Garrett wrote:

On Wed, Aug 04, 2010 at 11:30:44AM -0700, david@xxxxxxx wrote:
a couple days ago I made the suggestion to put non-privilaged tasks in a
cgroup so that the idle/suspend decision code could ignore acitivity
caused by this cgroup.

in the second version wakeup events would be 'activity' that would be
counted and therefor the system would not be idle. As for the race with
suspending and new things happening, wouldn't that be handled the same
way that it is in a normal linux box?

No! And that's precisely the issue. Android's existing behaviour could
be entirely implemented in the form of binary that manually triggers
suspend when (a) the screen is off and (b) no userspace applications
have indicated that the system shouldn't sleep, except for the wakeup
event race. Imagine the following:

1) The policy timeout is about to expire. No applications are holding
wakelocks. The system will suspend providing nothing takes a wakelock.
2) A network packet arrives indicating an incoming SIP call
3) The VOIP application takes a wakelock and prevents the phone from
suspending while the call is in progress

What stops the system going to sleep between (2) and (3)? cgroups don't,
because the voip app is an otherwise untrusted application that you've
just told the scheduler to ignore.

Even in the current implementation (wakelocks), Since the VOIP application isn't allowed to take a wakelock, wouldn't the system go to sleep immediatly anyway, even if the application gets the packet and starts the call? What would ever raise the wakelock to keep the phone from sleeping in the middle of the call?

as I said last night in an e-mail to Arve

it's possible that I'm making false assumptions about how quickly you want to go into full suspend mode.

if a user is doing nothing that would warrent wakelocks, but has an unprivilaged application running (a dancing cows game), and is doing nothing other than occasionally hitting a button, how short is the timeout that you would set that would have the system go into suspend? (i.e. how frequently must the user do something to keep the system awake)

or let's use a better example, the user has an unprivilaged book-reader application, how quickly must they change pages to prevent the system from suspending?

I'm figuring that these times are in the 1-5 minute range.

therefor the timeout period I am mentioning above could easily be one wakeup every 40-50 seconds. that is not going to kill your idle power.

is my assumption about the length of the timeout incorrect?

David Lang
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at