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    SubjectRe: [PATCH 03/16] blkio: Keep queue on service tree until we expire it
    On Fri, Nov 13 2009, Corrado Zoccolo wrote:
    > Hi Vivek,
    > the following is probably not on a critical path, but maybe it can be
    > written more efficiently.
    > Now, it will cicle through all service trees multiple times, to
    > retrieve the queues for the last one.
    > What about having a cfq_for_each_queue that takes a function pointer
    > and will apply it to all of them?

    I thought the same when reading this. Or perhaps have a small bitmap
    instead/with the counter to avoid looping around known empty groups.

    I want to start merging the initial prep patches soon, so we can both
    cut back on the size of your patchset while getting the simpler bits in.
    Unfortunately I had to stop here, but with a few corrections it can be
    merged too.

    >
    > On Fri, Nov 13, 2009 at 12:32 AM, Vivek Goyal <vgoyal@redhat.com> wrote:
    > > +static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
    > > +{
    > > +       struct cfq_group *cfqg = &cfqd->root_group;
    > > +       struct cfq_queue *cfqq;
    > > +       int i, j;
    > > +
    > > +       if (!cfqd->rq_queued)
    > > +               return NULL;
    > > +
    > > +       for (i = 0; i < 2; ++i) {
    > > +               for (j = 0; j < 3; ++j) {
    > > +                       cfqq = cfq_rb_first(&cfqg->service_trees[i][j]);
    > > +                       if (cfqq)
    > > +                               return cfqq;
    > > +               }
    > > +       }
    > > +
    > > +       cfqq = cfq_rb_first(&cfqg->service_tree_idle);
    > > +       if (cfqq)
    > > +               return cfqq;
    > > +       return NULL;
    > > +}
    > > +
    > >  /*
    > >  * Get and set a new active queue for service.
    > >  */
    > > @@ -1590,16 +1633,8 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd)
    > >  {
    > >        struct cfq_queue *cfqq;
    > >        int dispatched = 0;
    > > -       int i, j;
    > > -       struct cfq_group *cfqg = &cfqd->root_group;
    > > -
    > > -       for (i = 0; i < 2; ++i)
    > > -               for (j = 0; j < 3; ++j)
    > > -                       while ((cfqq = cfq_rb_first(&cfqg->service_trees[i][j]))
    > > -                               != NULL)
    > > -                               dispatched += __cfq_forced_dispatch_cfqq(cfqq);
    > >
    > > -       while ((cfqq = cfq_rb_first(&cfqg->service_tree_idle)) != NULL)
    > > +       while ((cfqq = cfq_get_next_queue(cfqd)) != NULL)
    > >                dispatched += __cfq_forced_dispatch_cfqq(cfqq);
    > >
    > >        cfq_slice_expired(cfqd, 0);
    > > @@ -1770,13 +1805,14 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
    > >        cfq_log_cfqq(cfqd, cfqq, "put_queue");
    > >        BUG_ON(rb_first(&cfqq->sort_list));
    > >        BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
    > > -       BUG_ON(cfq_cfqq_on_rr(cfqq));
    > >
    > >        if (unlikely(cfqd->active_queue == cfqq)) {
    > >                __cfq_slice_expired(cfqd, cfqq, 0);
    > >                cfq_schedule_dispatch(cfqd);
    > >        }
    > >
    > > +       BUG_ON(cfq_cfqq_on_rr(cfqq));
    > > +
    > >        kmem_cache_free(cfq_pool, cfqq);
    > >  }
    > >
    > > --
    > > 1.6.2.5
    > >
    >
    >
    >
    > Thanks
    > Corrado

    --
    Jens Axboe

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