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    SubjectRe: CFS and suspend2: hang in atomic copy (was: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS])

    * Christian Hesse <mail@earthworm.de> wrote:

    > Hi Ingo and all,
    >
    > On Friday 13 April 2007, Ingo Molnar wrote:
    > > as usual, any sort of feedback, bugreports, fixes and suggestions are
    > > more than welcome,
    >
    > I just gave CFS a try on my system. From a user's point of view it
    > looks good so far. Thanks for your work.

    you are welcome!

    > However I found a problem: When trying to suspend a system patched
    > with suspend2 2.2.9.11 it hangs with "doing atomic copy". Pressing the
    > ESC key results in a message that it tries to abort suspend, but then
    > still hangs.

    i took a quick look at suspend2 and it makes some use of yield().
    There's a bug in CFS's yield code, i've attached a patch that should fix
    it, does it make any difference to the hang?

    Ingo

    Index: linux/kernel/sched_fair.c
    ===================================================================
    --- linux.orig/kernel/sched_fair.c
    +++ linux/kernel/sched_fair.c
    @@ -264,15 +264,26 @@ static void dequeue_task_fair(struct rq

    /*
    * sched_yield() support is very simple via the rbtree, we just
    - * dequeue and enqueue the task, which causes the task to
    - * roundrobin to the end of the tree:
    + * dequeue the task and move it to the rightmost position, which
    + * causes the task to roundrobin to the end of the tree.
    */
    static void requeue_task_fair(struct rq *rq, struct task_struct *p)
    {
    dequeue_task_fair(rq, p);
    p->on_rq = 0;
    - enqueue_task_fair(rq, p);
    + /*
    + * Temporarily insert at the last position of the tree:
    + */
    + p->fair_key = LLONG_MAX;
    + __enqueue_task_fair(rq, p);
    p->on_rq = 1;
    +
    + /*
    + * Update the key to the real value, so that when all other
    + * tasks from before the rightmost position have executed,
    + * this task is picked up again:
    + */
    + p->fair_key = rq->fair_clock - p->wait_runtime + p->nice_offset;
    }

    /*
    @@ -380,7 +391,10 @@ static void task_tick_fair(struct rq *rq
    * Dequeue and enqueue the task to update its
    * position within the tree:
    */
    - requeue_task_fair(rq, curr);
    + dequeue_task_fair(rq, curr);
    + curr->on_rq = 0;
    + enqueue_task_fair(rq, curr);
    + curr->on_rq = 1;

    /*
    * Reschedule if another task tops the current one.
    -
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