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    SubjectRe: [linux-pm] [PATCH 0/8] Suspend block api (version 8)
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    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!




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