events/0 thread in kernels 2.6.22*fc6 causing scheduling latency
Fernando Apesteguía
fernando.apesteguia at gmail.com
Tue Aug 28 05:54:56 UTC 2007
On 8/27/07, Mike Fleetwood <mike.fleetwood at googlemail.com> wrote:
> Hi,
>
> Since I upgraded my FC6 box from kernel-2.6.20-1.2962.fc6 to
> kernel-2.6.22.1-32.fc6, and now 2.6.22.2-42.fc6, I am getting pauses
> from the whole OS. They last ~1 second and occur every few minutes.
> Every application becomes unresponsive for the duration. The 1 second
> scheduler latency this causes is long enough for my music player to be
> effected and the audio track to be interrupted. This makes the fault
> very easy to hear. At the same time kernel thread events/0 seems to
> use all the CPU time. Here is the first few lines of top's output
> when a pause happens:
> top - 21:39:41 up 1:17, 2 users, load average: 1.05, 1.20, 1.24
> Tasks: 138 total, 4 running, 134 sleeping, 0 stopped, 0 zombie
> Cpu(s): 2.3%us, 29.3%sy, 68.4%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
> Mem: 2074880k total, 1355244k used, 719636k free, 62144k buffers
> Swap: 1004052k total, 0k used, 1004052k free, 882684k cached
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 5525 mike 39 19 202m 81m 4016 R 68.4 4.0 13:07.46 hadcm3transum_5
> 6 root 15 -5 0 0 0 S 28.5 0.0 0:53.40 events/0
> 3619 mike 20 0 45620 8264 5856 S 0.9 0.4 0:18.58 xmms
> 3318 root 20 0 328m 46m 8132 S 0.6 2.3 1:39.60 Xorg
> 3524 mike 20 0 76728 23m 9640 S 0.6 1.2 1:13.15 bittorrent
> 3557 mike 20 0 211m 115m 30m S 0.6 5.7 3:54.24 firefox-bin
> 3489 mike 20 0 57240 23m 15m S 0.3 1.1 0:04.02 gnome-terminal
> 5583 root 20 0 2204 1100 832 R 0.3 0.1 0:01.14 top
> 28.5% CPU time used by events/0 of a single 3 second top refresh is
> 0.85 seconds of CPU time. Rebooting back to kernel 2.6.20 completely
> fixes it.
>
> Has any one else seen this issue?
> Does anyone know what kernel thread events/0 does?
It's a per processor work queue. This is a data structure used to
handle deferred work. As you have only one processor, you get an
events/0 (events/1, etc.. in SMP).
I've never seen that thread taking so much cpu time... maybe a kernel
developer can throw some light here
> Could this be related to CFS newly introduced into Fedora's kernel 2.6.22?
> Can anybody suggest how to fix this issue?
>
> Thanks,
> Mike
>
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