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    SubjectRe: performance regression from block merge
    On Thu, 21 Dec 2006 20:47:41 +0100
    Jens Axboe <jens.axboe@oracle.com> wrote:

    > On Thu, Dec 21 2006, Jens Axboe wrote:
    > > On Thu, Dec 21 2006, Andrew Morton wrote:
    > > >
    > > > Jens, elapsed time for `mke2fs /dev/hdc5' with the anticipatory scheduler
    > > > (at least) has gone from nine seconds to sixty as a result of the recent
    > > > block merge.
    > >
    > > About when? I'll double check and test here, I'm assuming you mean since
    > > 2.6.19?

    In yesterday's merge. I double-checked by testing yesterday's-Linus versus
    yesterday's-Linus-plus-yesterday's-git-block. The latter was slow.

    > Auch, brown paper bag time, I spotted an obvious typo in the recent
    > merge. Does this fix it? It should be safe to kill the ->special check,
    > but lets leave that for another time.
    >
    > diff --git a/block/elevator.c b/block/elevator.c
    > index 62c7a30..536be74 100644
    > --- a/block/elevator.c
    > +++ b/block/elevator.c
    > @@ -82,7 +82,7 @@ inline int elv_rq_merge_ok(struct reques
    > /*
    > * must be same device and not a special request
    > */
    > - if (rq->rq_disk != bio->bi_bdev->bd_disk || !rq->special)
    > + if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
    > return 0;
    >
    > if (!elv_iosched_allow_merge(rq, bio))
    >

    I shan't be near that machine for eight hours or so; shall test then.
    -
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