Package: linux-image-2.6.24-etchnhalf
Severity: normal
We upgraded to this kernel on a Dell PowerEdge server with a Dell PERC 6
RAID controller. This uses the megaraid_sas module.
Under even small amounts of load the RAID then generated so much iowait
the system was unusable. This was easily repeatable and very seriously
nasty. We experienced no problems under the previous 2.6.18-6 kernel.
You can see an example from top here:
Tasks: 127 total, 1 running, 126 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 74.3%id, 25.7%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 8307748k total, 3476056k used, 4831692k free, 10332k buffers
Swap: 2000084k total, 0k used, 2000084k free, 793932k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 1940 632 540 S 0 0.0 0:01.48 init
2 root 15 -5 0 0 0 S 0 0.0 0:00.00 kthreadd
3 root RT -5 0 0 0 S 0 0.0 0:00.00 migration/0
4 root 15 -5 0 0 0 S 0 0.0 0:00.00 ksoftirqd/0
5 root RT -5 0 0 0 S 0 0.0 0:00.00 watchdog/0
6 root RT -5 0 0 0 S 0 0.0 0:00.00 migration/1
7 root 15 -5 0 0 0 S 0 0.0 0:00.00 ksoftirqd/1
8 root RT -5 0 0 0 S 0 0.0 0:00.00 watchdog/1
iowait got as high as 70% on a basically idle system.
Here's some output from iostat:
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz
await svctm %util
sda 0.00 69.65 0.00 0.00 0.00 0.00 0.00 78.34
0.00 0.00 99.50
avg-cpu: %user %nice %system %iowait %steal %idle
6.94 0.00 0.25 34.58 0.00 58.23
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz
await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 159.00
0.00 0.00 100.00
avg-cpu: %user %nice %system %iowait %steal %idle
1.64 0.00 0.19 48.96 0.00 49.21
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz
await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 158.56
0.00 0.00 99.50
Again, whilst basically idle the utilisation is showing as 99.5%. Utilisation
at times went well over 100%, to perhaps 120%.
We've gone back to the previous kernel and now experience no problems.
Cheers,
Doug.
-- System Information:
Debian Release: 4.0
APT prefers proposed-updates
APT policy: (500, 'proposed-updates'), (500, 'stable')
Architecture: i386 (i686)
Shell: /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-6-686-bigmem
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
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