Messages in this thread | | | Subject | Re: [PATCH 3/3] sched, fair: Stop searching for tasks in newidle balance if there are runnable tasks | From | Mike Galbraith <> | Date | Thu, 24 Apr 2014 04:51:28 +0200 |
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On Wed, 2014-04-23 at 18:30 -0700, Jason Low wrote: > It was found that when running some workloads (such as AIM7) on large systems > with many cores, CPUs do not remain idle for long. Thus, tasks can > wake/get enqueued while doing idle balancing. > > In this patch, while traversing the domains in idle balance, in addition to > checking for pulled_task, we add an extra check for this_rq->nr_running for > determining if we should stop searching for tasks to pull. If there are > runnable tasks on this rq, then we will stop traversing the domains. This > reduces the chance that idle balance delays a task from running. > > This patch resulted in approximately a 6% performance improvement when > running a Java Server workload on an 8 socket machine.
Checking rq->lock for contention before ever going to idle balancing as well should give you a bit more. No need to run around looking for work that's trying to arrive. By not going there, perhaps stacking tasks, you may head off a future bounce as well.
-Mike
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