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    SubjectRe: [RFC][PATCH] create workqueue threads only when needed
    Benjamin Herrenschmidt wrote:
    > On Mon, 2009-02-02 at 03:24 +0100, Frederic Weisbecker wrote:
    >> 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.

    I rather suspect that the majority of private workqueues are there for
    good reasons.

    >> > 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:
    > That's not quite what I meant ...
    > The main problem with keventd I'd say is that it's used in all sort of
    > exeptional code path (ie, driver reset path, error handling, etc...) for
    > things that will msleep happily for tenth milliseconds, that sort of
    > thing.
    > IE. It will be pretty responsive -in general- but can suffer form
    > horrible latencies every now and then.

    Actually it /should/ be the other way around:

    The shared workqueue should only be used for work that sleeps only
    briefly (perhaps with the exception of very unlikely longer sleeps e.g.
    for allocations that cause paging).

    Work which /may/ sleep longer, for example performs SCSI transactions,
    needs to go into a private workqueue or other kind of context.

    OTOH you are right too; work which must not be deferred too long by work
    from another uncooperative/ unfair subsystem is probably also better off
    in an own workqueue...
    Stefan Richter
    -=====-==--= --=- ---=-

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