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    SubjectApp blocked in futex() burns 14% CPU.
    So, I've recently started enabling the KDE desktop search on my box and it 
    runs some indexing services (naturally) to keep track of changes to files.
    One of the apps it starts is a process named "virtuoso-t". This process
    burns a *lot* of CPU when it's just started, but once it has caught up
    with recent changes it quiets down. It doesn't quite quiet down to the
    level I'd expect though. I see it constantly using 12-14% CPU time in
    'top' even when there is *nothing* going on on the machine :

    top - 00:25:09 up 2:38, 2 users, load average: 0.01, 0.04, 0.05
    Tasks: 155 total, 1 running, 153 sleeping, 0 stopped, 1 zombie
    Cpu(s): 0.7%us, 0.8%sy, 3.7%ni, 94.6%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st
    Mem: 3853028k total, 2154696k used, 1698332k free, 184280k buffers
    Swap: 4200992k total, 0k used, 4200992k free, 996824k cached

    1952 jj 39 19 362m 263m 6544 S 14 7.0 25:09.54 virtuoso-t
    1811 jj 20 0 635m 27m 17m S 2 0.7 2:49.78 knotify4
    1928 jj 39 19 595m 26m 18m S 1 0.7 2:58.40 nepomukservices

    This box has a dual core Intel core i5-560M CPU with hyperthreading, so it
    is 12-14% of a fairly capable CPU - that's rather a lot more than I'd
    expect when the box is idle and there's nothing for the process to do.

    So, I tried strace'ing the process and it seems to just be blocked in
    futex() most of the time (like 99%) :

    [jj@dragon ~]$ strace -p 1952
    Process 1952 attached - interrupt to quit
    futex(0x3086424, FUTEX_WAIT_PRIVATE, 503, NULL

    So it's just sitting there doing nothing, which lead me to think that this
    is probably not a bug in the application - if it was doing some silly
    polling loop or similar I would not just see it blocked in a futex() call.
    So I'm guessing something must be happening in kernel space that's burning
    a lot of CPU.. I could be completely wrong of course, and if I am, please
    feel free to enlighten me.

    At this point I mainly want to know if I'm the only one seeing this and if
    someone has a good explanation for this, before I try to dig deeper into
    it myself.
    So, any ideas/explanations?

    Jesper Juhl <>
    Don't top-post
    Plain text mails only, please.

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