Messages in this thread | | | Subject | Re: [PATCH 3/3] sched, fair: Stop searching for tasks in newidle balance if there are runnable tasks | From | Jason Low <> | Date | Thu, 24 Apr 2014 09:37:52 -0700 |
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On Thu, 2014-04-24 at 04:51 +0200, Mike Galbraith wrote: > 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.
Are you thinking of something along the lines of this:
@@ -6658,7 +6658,8 @@ static int idle_balance(struct rq *this_rq) */ this_rq->idle_stamp = rq_clock(this_rq);
- if (this_rq->avg_idle < sysctl_sched_migration_cost) + if (this_rq->avg_idle < sysctl_sched_migration_cost || + spin_is_contended(&this_rq->lock)) goto out;
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