Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751380Ab1BXFUt (ORCPT ); Thu, 24 Feb 2011 00:20:49 -0500 Received: from e23smtp02.au.ibm.com ([202.81.31.144]:53751 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750887Ab1BXFUs (ORCPT ); Thu, 24 Feb 2011 00:20:48 -0500 Date: Thu, 24 Feb 2011 10:51:01 +0530 From: Bharata B Rao To: Peter Zijlstra Cc: Paul Turner , linux-kernel@vger.kernel.org, Dhaval Giani , Balbir Singh , Vaidyanathan Srinivasan , Srivatsa Vaddagiri , Kamalesh Babulal , Ingo Molnar , Pavel Emelyanov , Herbert Poetzl , Avi Kivity , Chris Friesen , Nikhil Rao Subject: Re: [CFS Bandwidth Control v4 3/7] sched: throttle cfs_rq entities which exceed their local quota Message-ID: <20110224052101.GA2755@in.ibm.com> Reply-To: bharata@linux.vnet.ibm.com References: <20110216031831.571628191@google.com> <20110216031841.068673650@google.com> <1298467933.2217.765.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1298467933.2217.765.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2644 Lines: 69 Hi Peter, I will only answer a couple of your questions and let Paul clarify the rest... On Wed, Feb 23, 2011 at 02:32:13PM +0100, Peter Zijlstra wrote: > On Tue, 2011-02-15 at 19:18 -0800, Paul Turner wrote: > > > > @@ -1363,6 +1407,9 @@ enqueue_task_fair(struct rq *rq, struct > > break; > > cfs_rq = cfs_rq_of(se); > > enqueue_entity(cfs_rq, se, flags); > > + /* don't continue to enqueue if our parent is throttled */ > > + if (cfs_rq_throttled(cfs_rq)) > > + break; > > flags = ENQUEUE_WAKEUP; > > } > > > > @@ -1390,8 +1437,11 @@ static void dequeue_task_fair(struct rq > > cfs_rq = cfs_rq_of(se); > > dequeue_entity(cfs_rq, se, flags); > > > > - /* Don't dequeue parent if it has other entities besides us */ > > - if (cfs_rq->load.weight) > > + /* > > + * Don't dequeue parent if it has other entities besides us, > > + * or if it is throttled > > + */ > > + if (cfs_rq->load.weight || cfs_rq_throttled(cfs_rq)) > > break; > > flags |= DEQUEUE_SLEEP; > > } > > How could we even be running if our parent was throttled? The task isn't running actually. One of its parents up in the heirarchy has been throttled and been already dequeued. Now this task sits on its immediate parent's runqueue which isn't throttled but not really running also since the hierarchy is throttled. In this situation, load balancer can try to pull this task. When that happens, load balancer tries to dequeue it and this check will ensure that we don't attempt to dequeue a group entity in our hierarchy which has already been dequeued. > > @@ -1438,10 +1524,16 @@ static void account_cfs_rq_quota(struct > > > > cfs_rq->quota_used += delta_exec; > > > > - if (cfs_rq->quota_used < cfs_rq->quota_assigned) > > + if (cfs_rq_throttled(cfs_rq) || > > + cfs_rq->quota_used < cfs_rq->quota_assigned) > > return; > > So we are throttled but running anyway, I suppose this comes from the PI > ceiling muck? When a cfs_rq is throttled, its representative se (and all its parent se's) get dequeued and the task is marked for resched. But the task entity is still on its throttled parent's cfs_rq (=> task->se.on_rq = 1). Next during put_prev_task_fair(), we enqueue the task back on its throttled parent's cfs_rq at which time we end up calling update_curr() on throttled cfs_rq. This check would help us bail out from that situation. Regards, Bharata. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/