Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759286AbYHZRh6 (ORCPT ); Tue, 26 Aug 2008 13:37:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757562AbYHZRhP (ORCPT ); Tue, 26 Aug 2008 13:37:15 -0400 Received: from 75-130-108-43.dhcp.oxfr.ma.charter.com ([75.130.108.43]:54161 "EHLO dev.haskins.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757369AbYHZRhM (ORCPT ); Tue, 26 Aug 2008 13:37:12 -0400 From: Gregory Haskins Subject: [PATCH v2 2/6] sched: pull only one task during NEWIDLE balancing to limit critical section To: mingo@elte.hu Cc: srostedt@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, npiggin@suse.de, gregory.haskins@gmail.com Date: Tue, 26 Aug 2008 13:34:54 -0400 Message-ID: <20080826173454.16413.10021.stgit@dev.haskins.net> In-Reply-To: <20080826173131.16413.17862.stgit@dev.haskins.net> References: <20080826173131.16413.17862.stgit@dev.haskins.net> User-Agent: StGIT/0.14.2 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1926 Lines: 59 git-id c4acb2c0669c5c5c9b28e9d02a34b5c67edf7092 attempted to limit newidle critical section length by stopping after at least one task was moved. Further investigation has shown that there are other paths nested further inside the algorithm which still remain that allow long latencies to occur with newidle balancing. This patch applies the same technique inside balance_tasks() to limit the duration of this optional balancing operation. Signed-off-by: Gregory Haskins CC: Nick Piggin --- kernel/sched.c | 18 +++++++++++++++++- 1 files changed, 17 insertions(+), 1 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 6a43c89..df6b447 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2962,6 +2962,16 @@ next: pulled++; rem_load_move -= p->se.load.weight; +#ifdef CONFIG_PREEMPT + /* + * NEWIDLE balancing is a source of latency, so preemptible kernels + * will stop after the first task is pulled to minimize the critical + * section. + */ + if (idle == CPU_NEWLY_IDLE) + goto out; +#endif + /* * We only want to steal up to the prescribed amount of weighted load. */ @@ -3008,9 +3018,15 @@ static int move_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest, sd, idle, all_pinned, &this_best_prio); class = class->next; +#ifdef CONFIG_PREEMPT + /* + * NEWIDLE balancing is a source of latency, so preemptible + * kernels will stop after the first task is pulled to minimize + * the critical section. + */ if (idle == CPU_NEWLY_IDLE && this_rq->nr_running) break; - +#endif } while (class && max_load_move > total_load_moved); return total_load_moved > 0; -- 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/