On Mon, 2011-04-11 at 10:46 +0000, tip-bot for Ken Chen wrote: > Commit-ID: b0432d8f162c7d5d9537b4cb749d44076b76a783 > Gitweb: http://git.kernel.org/tip/b0432d8f162c7d5d9537b4cb749d44076b76a783 > Author: Ken Chen <kenchen@xxxxxxxxxx> > AuthorDate: Thu, 7 Apr 2011 17:23:22 -0700 > Committer: Ingo Molnar <mingo@xxxxxxx> > CommitDate: Mon, 11 Apr 2011 11:08:54 +0200 > > sched: Fix sched-domain avg_load calculation > > In function find_busiest_group(), the sched-domain avg_load isn't > calculated at all if there is a group imbalance within the domain. This > will cause erroneous imbalance calculation. > > The reason is that calculate_imbalance() sees sds->avg_load = 0 and it > will dump entire sds->max_load into imbalance variable, which is used > later on to migrate entire load from busiest CPU to the puller CPU. > > This has two really bad effect: > > 1. stampede of task migration, and they won't be able to break out > of the bad state because of positive feedback loop: large load > delta -> heavier load migration -> larger imbalance and the cycle > goes on. > > 2. severe imbalance in CPU queue depth. This causes really long > scheduling latency blip which affects badly on application that > has tight latency requirement. > > The fix is to have kernel calculate domain avg_load in both cases. This > will ensure that imbalance calculation is always sensible and the target > is usually half way between busiest and puller CPU. > > Signed-off-by: Ken Chen <kenchen@xxxxxxxxxx> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > Cc: <stable@xxxxxxxxxx> > Link: http://lkml.kernel.org/r/20110408002322.3A0D812217F@xxxxxxxxxxxxxxxxxxx > Signed-off-by: Ingo Molnar <mingo@xxxxxxx> This was caused by 866ab43ef (sched: Fix the group_imb logic) which is only in .39-rc. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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