Kernel 3.2.0-33 Introduces Ridiculous / Impossible Load Averages
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
linux (Ubuntu) |
Fix Released
|
Medium
|
Unassigned |
Bug Description
After upgrading to the 3.2.0-33 kernel, our load averages have been very, very odd. Here is a sample sar -q line:
15:05:02 runq-sz plist-sz ldavg-1 ldavg-5 ldavg-15 blocked
15:05:21 2 322 44.02 12.51 14.08 1
A run queue size of 2, with a load average of 44? So I wrote a script to track run queue and uninterruptable sleep, since both contribute to load average. Script is attached. Sample output during a run:
Stat Time Run+Sleep Load Avg
2012-11-28 15:47:53 2 71.54
2012-11-28 15:47:54 1 71.54
2012-11-28 15:47:55 1 71.54
2012-11-28 15:47:56 1 71.54
2012-11-28 15:47:57 1 71.54
2012-11-28 15:47:58 1 65.81
This behavior is not observed with kernel 3.2.0-31.
Problem can be reproduced with a basic pgbench test to simulate busy state, but only seems to occur during rapid process cycling. An easy simulation:
for x in {1..100}; do
pgbench -T 5 -j 2 -c 2 pgbench
sleep 1
done
Test may need to run for several minutes to trigger load spike. It will look similar to this:
Stat Time Run+Sleep Load Avg
2012-11-28 16:01:17 3 10.37
2012-11-28 16:01:18 3 9.54
2012-11-28 16:01:19 3 9.54
2012-11-28 16:01:20 2 9.54
2012-11-28 16:01:21 5 9.54
2012-11-28 16:01:22 3 9.54
2012-11-28 16:01:23 1 47.94
System info:
Description: Ubuntu 12.04.1 LTS
Release: 12.04
Linux 3.2.0-33-generic #52-Ubuntu SMP Thu Oct 18 16:29:15 UTC 2012 x86_64
linux-image-
Installed: 3.2.0-33.52
tags: | removed: kernel-fixed-upstream |
tags: | added: kernel-fixed-upstream |
This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:
apport-collect 1084264
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.