The patch titled
NBD: make nbd default to deadline I/O scheduler
has been added to the -mm tree. Its filename is
nbd-make-nbd-default-to-deadline-i-o-scheduler.patch
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------------------------------------------------------
Subject: NBD: make nbd default to deadline I/O scheduler
From: Paul Clements <paul.clements@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/nbd.c | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN drivers/block/nbd.c~nbd-make-nbd-default-to-deadline-i-o-scheduler drivers/block/nbd.c
--- a/drivers/block/nbd.c~nbd-make-nbd-default-to-deadline-i-o-scheduler
+++ a/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")) {
_
Patches currently in -mm which might be from paul.clements@xxxxxxxxxxxx are
origin.patch
nbd-make-nbd-default-to-deadline-i-o-scheduler.patch
-
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