From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759274Ab0FRKTM (ORCPT ); Fri, 18 Jun 2010 06:19:12 -0400 Received: from hera.kernel.org ([140.211.167.34]:46934 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755890Ab0FRKTJ (ORCPT ); Fri, 18 Jun 2010 06:19:09 -0400 Date: Fri, 18 Jun 2010 10:18:32 GMT From: "tip-bot for Alex,Shi" Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, yanmin.zhang@intel.com, alex.shi@intel.com, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, yanmin.zhang@intel.com, tglx@linutronix.de, alex.shi@intel.com, mingo@elte.hu In-Reply-To: <1276754893.9452.5442.camel@debian> References: <1276754893.9452.5442.camel@debian> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched: Fix over-scheduling bug Message-ID: Git-Commit-ID: 3c93717cfa51316e4dbb471e7c0f9d243359d5f8 X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Fri, 18 Jun 2010 10:18:33 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 3c93717cfa51316e4dbb471e7c0f9d243359d5f8 Gitweb: http://git.kernel.org/tip/3c93717cfa51316e4dbb471e7c0f9d243359d5f8 Author: Alex,Shi AuthorDate: Thu, 17 Jun 2010 14:08:13 +0800 Committer: Ingo Molnar CommitDate: Fri, 18 Jun 2010 10:45:25 +0200 sched: Fix over-scheduling bug Commit e70971591 ("sched: Optimize unused cgroup configuration") introduced an imbalanced scheduling bug. If we do not use CGROUP, function update_h_load won't update h_load. When the system has a large number of tasks far more than logical CPU number, the incorrect cfs_rq[cpu]->h_load value will cause load_balance() to pull too many tasks to the local CPU from the busiest CPU. So the busiest CPU keeps going in a round robin. That will hurt performance. The issue was found originally by a scientific calculation workload that developed by Yanmin. With that commit, the workload performance drops about 40%. CPU before after 00 : 2 : 7 01 : 1 : 7 02 : 11 : 6 03 : 12 : 7 04 : 6 : 6 05 : 11 : 7 06 : 10 : 6 07 : 12 : 7 08 : 11 : 6 09 : 12 : 6 10 : 1 : 6 11 : 1 : 6 12 : 6 : 6 13 : 2 : 6 14 : 2 : 6 15 : 1 : 6 Reviewed-by: Yanmin zhang Signed-off-by: Alex Shi Signed-off-by: Peter Zijlstra LKML-Reference: <1276754893.9452.5442.camel@debian> Signed-off-by: Ingo Molnar --- kernel/sched.c | 3 --- 1 files changed, 0 insertions(+), 3 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 2aaceeb..6c9e7c8 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1657,9 +1657,6 @@ static void update_shares(struct sched_domain *sd) static void update_h_load(long cpu) { - if (root_task_group_empty()) - return; - walk_tg_tree(tg_load_down, tg_nop, (void *)cpu); }