Re: [RFD] Automatic suspend

Arve Hjønnevåg
2009-02-21T01:59:32Z

On Fri, Feb 20, 2009 at 3:20 PM, Oliver Neukum <oliver@neukum.org> wrote:
> Am Samstag 21 Februar 2009 00:11:28 schrieb Arve Hjønnevåg:
>> On Fri, Feb 20, 2009 at 2:05 PM, Oliver Neukum <oliver@neukum.org> wrote:
>> > Am Freitag 20 Februar 2009 11:46:55 schrieb Rafael J. Wysocki:
>> >> On Thursday 19 February 2009, Oliver Neukum wrote:
>
>> > With the set of runnable processes.There's always a window between
>> > evaluating the current set of runnable tasks and telling the kernel to
>> > sleep. IMO the most elegant solution would be a task attribute that would
>> > signal the kernel that a task should not count as keeping the system busy
>> > even if it is runnable and trigger the sleep in kernel space.
>>
>> It is not always safe to enter suspend when no tasks are runnable. For
>> instance, a key event could be on a user space queue, but the code
>> that reads from that queue has been paged out.
>
> In that case you'd have a task waiting for IO. The driver should refuse
> to suspend or wake up the system as IO is completed. It may be
> inefficient to suspend for such a presumably short time, but it is not
> a correctness issue.

In that case, yes. My point was that no-runnable-tasks is not a
sufficient indicator of whether suspend should fail or not. We have no
control of what a user space thread is waiting for though. It could be
waiting on a mutex that is locked by a thread that is marked not to
prevent suspend.

--
Arve Hjønnevåg