61 lines
1.8 KiB
Diff
61 lines
1.8 KiB
Diff
From: Alex,Shi <alex.shi@intel.com>
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Date: Thu, 17 Jun 2010 06:08:13 +0000 (+0800)
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Subject: sched: Fix over-scheduling bug
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X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=3c93717cfa51316e4dbb471e7c0f9d243359d5f8
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sched: Fix over-scheduling bug
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Commit e70971591 ("sched: Optimize unused cgroup configuration") introduced
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an imbalanced scheduling bug. [[ in 2.6.32-rc1 ]]
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If we do not use CGROUP, function update_h_load won't update h_load. When the
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system has a large number of tasks far more than logical CPU number, the
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incorrect cfs_rq[cpu]->h_load value will cause load_balance() to pull too
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many tasks to the local CPU from the busiest CPU. So the busiest CPU keeps
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going in a round robin. That will hurt performance.
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The issue was found originally by a scientific calculation workload that
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developed by Yanmin. With that commit, the workload performance drops
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about 40%.
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CPU before after
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00 : 2 : 7
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01 : 1 : 7
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02 : 11 : 6
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03 : 12 : 7
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04 : 6 : 6
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05 : 11 : 7
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06 : 10 : 6
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07 : 12 : 7
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08 : 11 : 6
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09 : 12 : 6
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10 : 1 : 6
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11 : 1 : 6
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12 : 6 : 6
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13 : 2 : 6
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14 : 2 : 6
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15 : 1 : 6
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Reviewed-by: Yanmin zhang <yanmin.zhang@intel.com>
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Signed-off-by: Alex Shi <alex.shi@intel.com>
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Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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LKML-Reference: <1276754893.9452.5442.camel@debian>
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Signed-off-by: Ingo Molnar <mingo@elte.hu>
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---
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diff --git a/kernel/sched.c b/kernel/sched.c
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index 2aaceeb..6c9e7c8 100644
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--- a/kernel/sched.c
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+++ b/kernel/sched.c
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@@ -1657,9 +1657,6 @@ static void update_shares(struct sched_domain *sd)
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static void update_h_load(long cpu)
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{
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- if (root_task_group_empty())
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- return;
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-
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walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
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}
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