Re: events/0 thread in kernels 2.6.22*fc6 causing scheduling latency

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On 8/27/07, Mike Fleetwood <mike.fleetwood@xxxxxxxxxxxxxx> 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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