Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755259AbXKGMRS (ORCPT ); Wed, 7 Nov 2007 07:17:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750882AbXKGMRK (ORCPT ); Wed, 7 Nov 2007 07:17:10 -0500 Received: from pentafluge.infradead.org ([213.146.154.40]:53748 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbXKGMRJ (ORCPT ); Wed, 7 Nov 2007 07:17:09 -0500 Subject: Re: [PATCH] sched: avoid large irq-latencies in smp-balancing From: Peter Zijlstra To: Ingo Molnar Cc: Peter Williams , linux-kernel In-Reply-To: <1194434956.6289.111.camel@twins> References: <1194434956.6289.111.camel@twins> Content-Type: text/plain Date: Wed, 07 Nov 2007 13:17:00 +0100 Message-Id: <1194437820.6289.114.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3536 Lines: 104 Bah, missed a hunk --- Subject: sched: avoid large irq-latencies in smp-balancing SMP balancing is done with IRQs disabled and can iterate the full rq. When rqs are large this can cause large irq-latencies. Limit the nr of iterations on each run. Signed-off-by: Peter Zijlstra CC: Peter Williams --- include/linux/sched.h | 1 + kernel/sched.c | 15 ++++++++++----- kernel/sysctl.c | 8 ++++++++ 3 files changed, 19 insertions(+), 5 deletions(-) Index: linux-2.6-2/kernel/sched.c =================================================================== --- linux-2.6-2.orig/kernel/sched.c +++ linux-2.6-2/kernel/sched.c @@ -474,6 +474,12 @@ const_debug unsigned int sysctl_sched_fe #define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x) /* + * Number of tasks to iterate in a single balance run. + * Limited because this is done with IRQs disabled. + */ +const_debug unsigned int sysctl_sched_nr_migrate = 32; + +/* * For kernel-internal use: high-speed (but slightly incorrect) per-cpu * clock constructed from sched_clock(): */ @@ -2237,7 +2243,7 @@ balance_tasks(struct rq *this_rq, int th enum cpu_idle_type idle, int *all_pinned, int *this_best_prio, struct rq_iterator *iterator) { - int pulled = 0, pinned = 0, skip_for_load; + int loops = 0, pulled = 0, pinned = 0, skip_for_load; struct task_struct *p; long rem_load_move = max_load_move; @@ -2251,10 +2257,10 @@ balance_tasks(struct rq *this_rq, int th */ p = iterator->start(iterator->arg); next: - if (!p) + if (!p || loops++ > sysctl_sched_nr_migrate) goto out; /* - * To help distribute high priority tasks accross CPUs we don't + * To help distribute high priority tasks across CPUs we don't * skip a task if it will be the highest priority task (i.e. smallest * prio value) on its new queue regardless of its load weight */ @@ -2271,8 +2277,7 @@ next: rem_load_move -= p->se.load.weight; /* - * We only want to steal up to the prescribed number of tasks - * and the prescribed amount of weighted load. + * We only want to steal up to the prescribed amount of weighted load. */ if (rem_load_move > 0) { if (p->prio < *this_best_prio) Index: linux-2.6-2/kernel/sysctl.c =================================================================== --- linux-2.6-2.orig/kernel/sysctl.c +++ linux-2.6-2/kernel/sysctl.c @@ -298,6 +298,14 @@ static struct ctl_table kern_table[] = { .mode = 0644, .proc_handler = &proc_dointvec, }, + { + .ctl_name = CTL_UNNUMBERED, + .procname = "sched_nr_migrate", + .data = &sysctl_sched_nr_migrate, + .maxlen = sizeof(unsigned int), + .mode = 644, + .proc_handler = &proc_dointvec, + }, #endif { .ctl_name = CTL_UNNUMBERED, Index: linux-2.6-2/include/linux/sched.h =================================================================== --- linux-2.6-2.orig/include/linux/sched.h +++ linux-2.6-2/include/linux/sched.h @@ -1466,6 +1466,7 @@ extern unsigned int sysctl_sched_batch_w extern unsigned int sysctl_sched_child_runs_first; extern unsigned int sysctl_sched_features; extern unsigned int sysctl_sched_migration_cost; +extern unsigned int sysctl_sched_nr_migrate; #endif extern unsigned int sysctl_sched_compat_yield; - 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/