From: Alex,Shi Date: Thu, 17 Jun 2010 06:08:13 +0000 (+0800) Subject: sched: Fix over-scheduling bug X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=3c93717cfa51316e4dbb471e7c0f9d243359d5f8 sched: Fix over-scheduling bug Commit e70971591 ("sched: Optimize unused cgroup configuration") introduced an imbalanced scheduling bug. [[ in 2.6.32-rc1 ]] 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 --- 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); }