linux-kernel - Re: performance regression from block merge

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Message-Id: <20061221121430.33392935.akpm@osdl.org>
Date:	Thu, 21 Dec 2006 12:14:30 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>
Subject: Re: performance regression from block merge

On Thu, 21 Dec 2006 20:47:41 +0100
Jens Axboe <jens.axboe@...cle.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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