Re: [linux-pm] [PATCH 1/8] PM: Add suspend block api.

[Arve Hjønnevåg]

On Fri, May 7, 2010 at 2:25 PM, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> * Matthew Garrett <mjg@xxxxxxxxxx> [100507 13:58]:
>> On Fri, May 07, 2010 at 01:53:29PM -0700, Tony Lindgren wrote:
>>
>> > So for example, if I leave ping running in a a terminal, do you
>> > have some way of preventing that from eating the battery?
>>
>> It depends on policy. If all network packets generate wakeup events then
>> no, that will carry on eating battery. If ICMP doesn't generate a wakeup
>> event then the process won't be run.
>>
>> > Do you just suspend the whole system anyways at some point,
>> > or do you have some other trick?
>>
>> If nothing's holding any suspend blocks then the system will enter
>> suspend. If the packet generates a wakeup then the kernel would block
>> suspend until userspace has had the opportunity to do so. Once userspace
>> has handled the packet then it could release the block and the system
>> will immediately transition back into suspend.
>
> OK, then what would I need to do to keep that ping running if I wanted to?
>

Use a suspend blocker. For instance: "runsuspendblock ping <addr>".

>> Here's a different example. A process is waiting for a keypress, but
>> because it's badly written it's also drawing to the screen at 60 frames
>> per second and preventing the system from every going to idle. How do
>> you quiesce the system while still ensuring that the keypress will be
>> delivered to the application?
>
> I guess it depends. If it's a game and I'm waiting to hit the fire
> button, then I don't want the system to suspend!
>

We don't suspend while the screen is on. If the user pressed the power
button to turn the screen off, then I would not want the game to
prevent suspend.

> It's starting to sound like you're really using suspend blocks
> to "certify" that the app is safe to keep running.
>
> Maybe it could be done with some kind of process flag instead that
> would tell "this process is safe to keep running from timer point of view"
> and if that flag is not set, then assume it's OK to stop the process
> at any point?
>
> Regards,
>
> Tony
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>



-- 
Arve Hjønnevåg
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