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    SubjectRe: [RFC][PATCH] create workqueue threads only when needed
    On Mon, Feb 02, 2009 at 08:37:41AM +1100, Benjamin Herrenschmidt wrote:
    >
    > > I don't know, most of those I've looked on are not documented about the reason
    > > for a private workqueue. I guess most of them can use the usual kevent.
    >
    > The main problem with kevent is that it gets clogged up.


    I don't think so. Here is a snapshot of the workqueue tracer in my
    box currently:

    # CPU INSERTED EXECUTED NAME
    # | | | |

    1 0 0 hda0/1
    1 589 589 reiserfs/1
    1 0 0 scsi_tgtd/1
    1 0 0 aio/1
    1 0 0 ata/1
    1 378 378 kblockd/1
    1 0 0 kintegrityd/1
    1 2 2 work_on_cpu/1
    1 8706 8706 events/1

    0 19994 19994 cqueue
    0 0 0 hda0/0
    0 501 501 reiserfs/0
    0 0 0 scsi_tgtd/0
    0 0 0 aio/0
    0 0 0 ata_aux
    0 0 0 ata/0
    0 4 4 kacpi_notify
    0 22 22 kacpid
    0 379 379 kblockd/0
    0 0 0 kintegrityd/0
    0 1056 1056 khelper
    0 15 15 work_on_cpu/0
    0 9367 9367 events/0
    0 0 0 cpuset

    And the result of uptime:

    02:51:40 up 2:22, 6 users, load average: 0.22, 0.34, 0.59

    So I have a total of 18073 works sent and performed by kevent for
    10300 seconds.

    An average of a bit less than 2 works on kevents per seconds is not about something
    clogged, especially since we are talking about small jobs, usually those which play
    the role of bottom halves and would have fit in a tasklet/softirq by the past.

    Now if you look at the other workqueues.
    Most of them don't do anything (more likely I don't do anything with them).

    Khelper can't be replaced since it performs slow works which may wait for userspace
    processes completion although I'm not sure it's still useful after the boot.

    cqueue is usually inactive but I raised a good number of events artificially on it, I
    just sent a patch to create its workqueue only when needed.

    And for the others, I don't know yet.


    > That's were thread pools kick in ... tried using Dave Howells slow
    > work ?


    I think it can be useful, as an example the kpsmoused workqueue receive rare
    and slow works of mouse resynchronisation.
    I wanted to convert it into a slow work created only on the fly.

    But..I don't find it. I've seen some patches about it but it doesn't seem
    to be merged.
    So I tried something else for kpsmoused: turn it into a thread created on the fly.

    But I think these slow works could be useful for such things.


    > Cheers,
    > Ben.
    >
    >



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