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Message-ID: <1398357472.3509.2.camel@j-VirtualBox>
Date: Thu, 24 Apr 2014 09:37:52 -0700
From: Jason Low <jason.low2@...com>
To: Mike Galbraith <umgwanakikbuti@...il.com>
Cc: mingo@...nel.org, peterz@...radead.org,
linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
alex.shi@...aro.org, preeti@...ux.vnet.ibm.com,
vincent.guittot@...aro.org, morten.rasmussen@....com, aswin@...com,
chegu_vinod@...com
Subject: Re: [PATCH 3/3] sched, fair: Stop searching for tasks in newidle
balance if there are runnable tasks
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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