From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754899AbaAFLjT (ORCPT ); Mon, 6 Jan 2014 06:39:19 -0500 Received: from cantor2.suse.de ([195.135.220.15]:36936 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752776AbaAFLjQ (ORCPT ); Mon, 6 Jan 2014 06:39:16 -0500 Date: Mon, 6 Jan 2014 11:39:12 +0000 From: Mel Gorman To: Peter Zijlstra Cc: Thomas Hellstrom , Rik van Riel , linux-kernel@vger.kernel.org Subject: [PATCH] sched: Calculate effective load even if local weight is 0 Message-ID: <20140106113912.GC6178@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (Rik, you authored this patch so it should be sent from you and needs a signed-off assuming people are ok with the changelog.) Thomas Hellstrom bisected a regression where erratic 3D performance is experienced on virtual machines as measured by glxgears. It identified commit 58d081b5 (sched/numa: Avoid overloading CPUs on a preferred NUMA node) as the problem which had modified the behaviour of effective_load. Effective load calculates the difference to the system-wide load if a scheduling entity was moved to another CPU. The task group is not heavier as a result of the move but overall system load can increase/decrease as a result of the change. Commit 58d081b5 (sched/numa: Avoid overloading CPUs on a preferred NUMA node) changed effective_load to make it suitable for calculating if a particular NUMA node was compute overloaded. To reduce the cost of the function, it assumed that a current sched entity weight of 0 was uninteresting but that is not the case. wake_affine uses a weight of 0 for sync wakeups on the grounds that it is assuming the waking task will sleep and not contribute to load in the near future. In this case, we still want to calculate the effective load of the sched entity hierarchy. As effective_load is no longer used by task_numa_compare since commit fb13c7ee (sched/numa: Use a system-wide search to find swap/migration candidates), this patch simply restores the historical behaviour. [mgorman@suse.de: Wrote changelog] Reported-and-tested-by: Thomas Hellstrom Should-be-signed-off-and-authored-by-Rik --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c7395d9..e64b079 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3923,7 +3923,7 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg) { struct sched_entity *se = tg->se[cpu]; - if (!tg->parent || !wl) /* the trivial, non-cgroup case */ + if (!tg->parent) /* the trivial, non-cgroup case */ return wl; for_each_sched_entity(se) {