lkml.org 
[lkml]   [2003]   [Jun]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] io stalls (was: -rc7 Re: Linux 2.4.21-rc6)
    On Wed, Jun 11, 2003 at 02:27:13PM -0400, Chris Mason wrote:
    > On Wed, 2003-06-11 at 14:12, Andrea Arcangeli wrote:
    > > On Wed, Jun 11, 2003 at 01:42:41PM -0400, Chris Mason wrote:
    > > > + if (q->rq[rw].count >= q->batch_requests) {
    > > > + smp_mb();
    > > > + if (waitqueue_active(&q->wait_for_requests[rw]))
    > > > + wake_up(&q->wait_for_requests[rw]);
    > >
    > > in my tree I also changed this to:
    > >
    > > wake_up_nr(&q->wait_for_requests[rw], q->rq[rw].count);
    > >
    > > otherwise only one waiter will eat the requests, while multiple waiters
    > > can eat requests in parallel instead because we freed not just 1 request
    > > but many of them.
    >
    > I tried a few variations of this yesterday and they all led to horrible
    > latencies, but I couldn't really explain why. I had a bunch of other

    the I/O latency in theory shouldn't change, we're not reordering the
    queue at all, they'll go to sleep immediatly again if __get_request
    returns null.

    > stuff in at the time to try and improve throughput though, so I'll try
    > it again.
    >
    > I think part of the problem is the cascading wakeups from
    > get_request_wait_wakeup(). So if we wakeup 32 procs they in turn wakeup
    > another 32, etc.

    so maybe it's enough to wakeup count / 2 to account for the double
    wakeup? that will avoid some overscheduling indeed.

    Andrea
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:36    [W:0.020 / U:30.204 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site