Re: [PATCH 0/8] Suspend block api (version 8)

Peter Zijlstra
2010-05-27T14:28:51Z

On Thu, 2010-05-27 at 15:06 +0100, Matthew Garrett wrote:

> I don't entirely see how this works. In order to deal with poorly
> written applications, it's necessary to (optionally, based on some
> policy) ignore them when it comes to the scheduler. The problem is how
> to implement the optional nature of this in a race-free manner. This is
> obviously a pathological case, but imagine an application that does
> something along the following lines:
>
> int input = open ("/dev/input", O_RDONLY|O_NONBLOCK);
> char foo;
>
> while (1) {
> suspend_block();
> if (read(input, &foo, 1) > 0) {
> (do something)
> suspend_unblock();
> } else {
> suspend_unblock();
> (draw bouncing cows and clouds and tractor beams briefly)
> }
> }
>
> Now, if the user is playing this game, you want it to be scheduled. If
> the user has put down their phone and the screen lock has kicked in, you
> don't want it to be scheduled. So we could imagine some sort of cgroup
> that contains untrusted tasks - when the session is active we set a flag
> one way which indicates to the scheduler that tasks in TASK_RUNNING
> should be scheduled, and when the session is idle we set the flag the
> other way and all processes in that cgroup get shifted to
> TASK_INTERRUPTIBLE or something.

What's wrong with simply making the phone beep loudly and displaying:
bouncing cows is preventing your phone from sleeping!