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From: Paul Clements <paul.clements@steeleye.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: jens.axboe@oracle.com, randy.dunlap@oracle.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] NBD: make nbd default to deadline I/O scheduler
Date: Sat, 09 Feb 2008 08:30:40 -0500	[thread overview]
Message-ID: <47ADAB00.90306@steeleye.com> (raw)
In-Reply-To: <20080208140244.c850a5d3.akpm@linux-foundation.org>

[-- Attachment #1: Type: text/plain, Size: 50 bytes --]


Take 3...this should address all the issues.





[-- Attachment #2: nbd_default_to_deadline_then_noop.diff --]
[-- Type: text/x-patch, Size: 1442 bytes --]

NBD doesn't work well with CFQ (or AS) schedulers, so let's default to something
else.

The two problems I have experienced with nbd and cfq are:
 
1) nbd hangs with cfq on RHEL 5 (2.6.18) -- this may well have been fixed
 
There's a similar debian bug that has been filed as well:
 
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=447638

There have been posts to nbd-general mailing list about problems with 
cfq and nbd also.
 
2) nbd performs about 10% better (the last time I tested) with deadline 
vs. cfq (the overhead of cfq doesn't provide much advantage to nbd [not 
being a real disk], and you end up going through the I/O scheduler on 
the nbd server anyway, so it makes sense that deadline is better with nbd)
 

Signed-Off-By: Paul Clements <paul.clements@steeleye.com>

--- ./drivers/block/nbd.c.max_nbd_killed	2008-02-07 16:46:24.000000000 -0500
+++ ./drivers/block/nbd.c	2008-02-09 08:14:18.000000000 -0500
@@ -654,6 +654,7 @@ static int __init nbd_init(void)
 
 	for (i = 0; i < nbds_max; i++) {
 		struct gendisk *disk = alloc_disk(1);
+		elevator_t *old_e;
 		if (!disk)
 			goto out;
 		nbd_dev[i].disk = disk;
@@ -667,6 +668,11 @@ static int __init nbd_init(void)
 			put_disk(disk);
 			goto out;
 		}
+		old_e = disk->queue->elevator;
+		if (elevator_init(disk->queue, "deadline") == 0 ||
+			elevator_init(disk->queue, "noop") == 0) {
+				elevator_exit(old_e);
+		}
 	}
 
 	if (register_blkdev(NBD_MAJOR, "nbd")) {

  reply	other threads:[~2008-02-09 13:30 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-08 16:47 Paul Clements
2008-02-08 17:33 ` Randy Dunlap
2008-02-08 18:11   ` Andrew Morton
2008-02-08 18:41     ` Paul Clements
2008-02-08 20:45       ` Jens Axboe
2008-02-08 20:47         ` Jens Axboe
2008-02-08 21:23           ` Paul Clements
2008-02-08 22:02             ` Andrew Morton
2008-02-09 13:30               ` Paul Clements [this message]
2008-02-12 23:16                 ` Andrew Morton
2008-02-18 18:16                   ` Jens Axboe
2008-02-18 23:50                     ` Andrew Morton
2008-02-19  9:19                       ` Jens Axboe
2008-02-19  9:24                         ` Jens Axboe
2008-02-19 10:02                           ` Andrew Morton
2008-02-19 10:05                             ` Jens Axboe
2008-02-08 22:45       ` [Nbd] " Mike Snitzer

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