linux-kernel - Re: performance regression from block merge

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Date:	Thu, 21 Dec 2006 20:47:41 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>
Subject: Re: performance regression from block merge

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?

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))

-- 
Jens Axboe

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