On Thu, Jul 23, 2015 at 06:42:12PM +0200, Frederic Weisbecker wrote: > Instead of providing asynchronous checks for the nohz subsystem to verify > sched tick dependency, migrate sched to the new mask. > > The easiest is to recycle the current asynchronous tick dependency check > which verifies the class of the current task and its requirements for > periodic preemption checks. > > We need to evaluate this tick dependency on three places: > > 1) Task enqueue: One or more tasks have been enqueued, we must check > if those are competing with the current task. > > 2) Task dequeue: A possibly competing task has been dequeued, clear the > tick dependency if needed. > > 3) schedule(): we might be switching to a task of another scheduler > class. Each class has its preemption rules, we must re-evaluate it.
This is insane.. You add a whole bunch of work per wakeup/sleep/context switch to avoid some work at tick time. That's a broken trade-off. We can context switch _waaaay_ more than we have ticks. Furthermore, you do tons of pointless work, we call add_nr_running() from the individual classes, and then your routine goes and checks what class we're in etc.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
