From 48f15b93b2c9f4ec9b8af08ab78f7a27db7c8378 Mon Sep 17 00:00:00 2001
From: Paul Clements <paul.clements@steeleye.com>
Date: Sat, 23 Feb 2008 15:23:50 -0800
Subject: [PATCH] NBD: make nbd default to deadline I/O scheduler
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>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
drivers/block/nbd.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 018753c59b8e..b53fdb0a282c 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -655,6 +655,7 @@ 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;
@@ -668,6 +669,11 @@ 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")) {
--
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