linux-kernel - Kernel migration thread cpu usage is crazy in 3.1.5

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Date:	Sun, 18 Dec 2011 19:16:44 +0200
From:	"Darius D." <darius.ski@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Kernel migration thread cpu usage is crazy in 3.1.5

Hi,


there has already been a report about migration thread CPU usage
craziness in 3.2 ( https://lkml.org/lkml/2011/11/17/375 ), but it is
in 3.1.5 as well.

problem manifests itself like this: after some time top/ps starts
reporting huge time for migration/X threads, adding them 1 at time
with larger and larger values (sometimes already existing entry is
"incremented" ), so after a while it looks like this:

   47 root      RT   0     0    0    0 S    0  0.0   1100:35 [migration/14]
   14 root      RT   0     0    0    0 S    0  0.0   1081:39 [migration/3]
   50 root      RT   0     0    0    0 S    0  0.0 978:44.59 [migration/15]
   53 root      RT   0     0    0    0 S    0  0.0 840:53.83 [migration/16]
   74 root      RT   0     0    0    0 S    0  0.0 779:58.12 [migration/23]
   44 root      RT   0     0    0    0 S    0  0.0 773:43.01 [migration/13]
   41 root      RT   0     0    0    0 S    0  0.0 539:50.44 [migration/12]
   59 root      RT   0     0    0    0 S    0  0.0 380:05.40 [migration/18]
   56 root      RT   0     0    0    0 S    0  0.0 293:07.90 [migration/17]
   68 root      RT   0     0    0    0 S    0  0.0 150:10.87 [migration/21]
   26 root      RT   0     0    0    0 S    0  0.0 145:13.37 [migration/7]
   11 root      RT   0     0    0    0 S    0  0.0 130:11.83 [migration/2]

sar and other tools are not showing any increased cpu activity ( no
misreporting, as box is under very low load and power usage would
shoot sky high if there was some well hidden cpu usage )


System is dual Xeon X5650 NUMA box. Last kernel it was running with
same kernel config was 2.6.39.2.
The only outside visible "change" i have noticed is this:
In munin graphs during low activity periods there were ~1k Local timer
interrupts, after booting 3.1.5 graphs are completely different, now
there are just ~500 Local timer interrupts, but Rescheduling
interrupts are ~400 ( used to be none on low load ). Is this related
to crazy cpu usage problem ?


Darius.
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