From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757083Ab3IONtZ (ORCPT ); Sun, 15 Sep 2013 09:49:25 -0400 Received: from relay.parallels.com ([195.214.232.42]:35167 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757052Ab3IONtY (ORCPT ); Sun, 15 Sep 2013 09:49:24 -0400 From: Vladimir Davydov To: Peter Zijlstra , Ingo Molnar CC: Paul Turner , , Subject: [PATCH 1/2] sched: calculate_imbalance: Fix local->avg_load > sds->avg_load case Date: Sun, 15 Sep 2013 17:49:13 +0400 Message-ID: <8f596cc6bc0e5e655119dc892c9bfcad26e971f4.1379252740.git.vdavydov@parallels.com> X-Mailer: git-send-email 1.7.10.4 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.24.21.58] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In busiest->group_imb case we can come to calculate_imbalance() with local->avg_load >= busiest->avg_load >= sds->avg_load. This can result in imbalance overflow, because it is calculated as follows env->imbalance = min( max_pull * busiest->group_power, (sds->avg_load - local->avg_load) * local->group_power ) / SCHED_POWER_SCALE; As a result we can end up constantly bouncing tasks from one cpu to another if there are pinned tasks. Fix this by skipping the assignment and assuming imbalance=0 in case local->avg_load > sds->avg_load. -- The bug can be caught by running 2*N cpuhogs pinned to two logical cpus belonging to different cores on an HT-enabled machine with N logical cpus: just look at se.nr_migrations growth. Signed-off-by: Vladimir Davydov --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9b3fe1c..507a8a9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4896,7 +4896,8 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s * max load less than avg load(as we skip the groups at or below * its cpu_power, while calculating max_load..) */ - if (busiest->avg_load < sds->avg_load) { + if (busiest->avg_load <= sds->avg_load || + local->avg_load >= sds->avg_load) { env->imbalance = 0; return fix_small_imbalance(env, sds); } -- 1.7.10.4