lkml.org 
[lkml]   [2010]   [Jul]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH] cfq-iosched: don't allow aliased requests to starve others
    Date
    Jeff Moyer <jmoyer@redhat.com> writes:

    > Hi,
    >
    > In running a test case that tries to trip up the kernel's AIO
    > implementation, we ran into a situation where no other I/O to the device
    > under test would be completed. The test program spawned (in this case)
    > 100 threads, each of which performed the following in a loop:
    >
    > open file O_DIRECT
    > queue 1MB of read I/O from file using 16 iocbs
    > close file
    > repeat
    >
    > The program does NOT wait for the I/O to complete. The file length is
    > only 4MB, meaning that you have 25 threads performing I/O on each of the
    > 4 1MB regions.
    >
    > Both deadline and cfq check for aliased requests in the sorted list of
    > I/Os, and when an alias is found, the request in the rb tree is moved to
    > the dispatch list. So, what happens is that, with this workload, only
    > requests from this program are moved to the dispatch list, starving out
    > all other I/O.
    >
    > The attached patch fixes this problem by issuing all expired requests in
    > the aliased request handling code. The reason I opted to issue all
    > expired requsts is because if we only service a single one, I still see
    > really awful interactivity; an ls would take over 5 minutes to
    > complete. With the attached patch, the ls took about 7 seconds to
    > complete.
    >
    > Comments, as always, are welcome.
    >
    > Cheers,
    > Jeff

    Forgot:

    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

    >
    > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
    > index 7982b83..0d8d2cd 100644
    > --- a/block/cfq-iosched.c
    > +++ b/block/cfq-iosched.c
    > @@ -417,6 +417,7 @@ static inline int cfqg_busy_async_queues(struct cfq_data *cfqd,
    > }
    >
    > static void cfq_dispatch_insert(struct request_queue *, struct request *);
    > +static struct request *cfq_check_fifo(struct cfq_queue *cfqq);
    > static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
    > struct io_context *, gfp_t);
    > static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
    > @@ -1394,10 +1395,22 @@ static void cfq_add_rq_rb(struct request *rq)
    >
    > /*
    > * looks a little odd, but the first insert might return an alias.
    > - * if that happens, put the alias on the dispatch list
    > + * If that happens, put the alias on the dispatch list, but don't
    > + * allow issuing of aliased requests to starve out the queue.
    > */
    > - while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)
    > + while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL) {
    > + int fifo_checked = cfq_cfqq_fifo_expire(cfqq);
    > + struct request *__rq;
    > +
    > cfq_dispatch_insert(cfqd->queue, __alias);
    > + cfq_clear_cfqq_fifo_expire(cfqq);
    > + while ((__rq = cfq_check_fifo(cfqq))) {
    > + cfq_dispatch_insert(cfqd->queue, __rq);
    > + cfq_clear_cfqq_fifo_expire(cfqq);
    > + }
    > + if (fifo_checked)
    > + cfq_mark_cfqq_fifo_expire(cfqq);
    > + }
    >
    > if (!cfq_cfqq_on_rr(cfqq))
    > cfq_add_cfqq_rr(cfqd, cfqq);
    > --
    > 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: 2010-07-14 21:03    [W:0.033 / U:92.196 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site