From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760044Ab0G3R4o (ORCPT ); Fri, 30 Jul 2010 13:56:44 -0400 Received: from kroah.org ([198.145.64.141]:58554 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759974Ab0G3Rzq (ORCPT ); Fri, 30 Jul 2010 13:55:46 -0400 X-Mailbox-Line: From gregkh@clark.site Fri Jul 30 10:51:41 2010 Message-Id: <20100730175141.715008212@clark.site> User-Agent: quilt/0.48-11.2 Date: Fri, 30 Jul 2010 10:51:46 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Alex Shi , Peter Zijlstra , Ingo Molnar Subject: [089/205] sched: Fix over-scheduling bug In-Reply-To: <20100730175238.GA3924@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.34-stable review patch. If anyone has any objections, please let us know. ------------------ From: Alex,Shi commit 3c93717cfa51316e4dbb471e7c0f9d243359d5f8 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 3 --- 1 file changed, 3 deletions(-) --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1675,9 +1675,6 @@ static void update_shares(struct sched_d static void update_h_load(long cpu) { - if (root_task_group_empty()) - return; - walk_tg_tree(tg_load_down, tg_nop, (void *)cpu); }