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authorAlex,Shi <alex.shi@intel.com>2010-06-17 14:08:13 +0800
committerIngo Molnar <mingo@elte.hu>2010-06-18 10:45:25 +0200
commit3c93717cfa51316e4dbb471e7c0f9d243359d5f8 (patch)
tree0c37ea18287556b42d6264d41c7093dd07f052f5 /kernel/sched.c
parentdc61b1d65e353d638b2445f71fb8e5b5630f2415 (diff)
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 <yanmin.zhang@intel.com> Signed-off-by: Alex Shi <alex.shi@intel.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1276754893.9452.5442.camel@debian> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c3
1 files changed, 0 insertions, 3 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 2aaceebd484..6c9e7c8735b 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);
}