From: Andrew Morton <akpm@zip.com.au>
To: Jens Axboe <axboe@suse.de>
Cc: William Lee Irwin III <wli@holomorphy.com>,
Giuliano Pochini <pochini@shiny.it>,
linux-kernel@vger.kernel.org, "chen,
xiangping" <chen_xiangping@emc.com>
Subject: Re: Poor read performance when sequential write presents
Date: Mon, 27 May 2002 01:22:41 -0700 [thread overview]
Message-ID: <3CF1ECD1.A1BB2CF1@zip.com.au> (raw)
In-Reply-To: <3CED4843.2783B568@zip.com.au> <XFMail.20020524105942.pochini@shiny.it> <3CEE0758.27110CAD@zip.com.au> <20020524094606.GH14918@holomorphy.com> <3CEE1035.1E67E1B8@zip.com.au> <20020527080632.GC17674@suse.de>
Jens Axboe wrote:
>
> ...
> > But in 2.5, head-activeness went away and as far as I know, IDE and SCSI are
> > treated the same. Odd.
>
> It didn't really go away, it just gets handled automatically now.
> elv_next_request() marks the request as started, in which case the i/o
> scheduler won't consider it for merging etc. SCSI removes the request
> directly after it has been marked started, while IDE leaves it on the
> queue until it completes. For IDE TCQ, the behaviour is the same as with
> SCSI.
It won't consider the active request at the head of the queue for
merging (making the request larger). But it _could_ consider the
request when making decisions about insertion (adding a new request
at the head of the queue because it's close-on-disk to the active
one). Does it do that?
-
next prev parent reply other threads:[~2002-05-27 8:19 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-05-23 14:20 Poor read performance when sequential write presents chen, xiangping
2002-05-23 19:51 ` Andrew Morton
2002-05-24 8:59 ` Giuliano Pochini
2002-05-24 9:26 ` Andrew Morton
2002-05-24 9:46 ` William Lee Irwin III
2002-05-24 10:04 ` Andrew Morton
2002-05-27 8:06 ` Jens Axboe
2002-05-27 8:22 ` Andrew Morton [this message]
2002-05-27 8:54 ` Jens Axboe
2002-05-27 9:35 ` Andrew Morton
2002-05-28 9:25 ` Jens Axboe
2002-05-28 9:36 ` Jens Axboe
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