| From 3c93717cfa51316e4dbb471e7c0f9d243359d5f8 Mon Sep 17 00:00:00 2001 |
| From: Alex,Shi <alex.shi@intel.com> |
| Date: Thu, 17 Jun 2010 14:08:13 +0800 |
| Subject: sched: Fix over-scheduling bug |
| |
| From: Alex,Shi <alex.shi@intel.com> |
| |
| 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 <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> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| kernel/sched.c | 3 --- |
| 1 file changed, 3 deletions(-) |
| |
| --- a/kernel/sched.c |
| +++ b/kernel/sched.c |
| @@ -1719,9 +1719,6 @@ static void update_shares_locked(struct |
| |
| static void update_h_load(long cpu) |
| { |
| - if (root_task_group_empty()) |
| - return; |
| - |
| walk_tg_tree(tg_load_down, tg_nop, (void *)cpu); |
| } |
| |
