Commit:     48f15b93b2c9f4ec9b8af08ab78f7a27db7c8378
Parent:     2f56debd77a8f52f1ac1d3c3d89cc7ce5e083230
Author:     Paul Clements <[EMAIL PROTECTED]>
AuthorDate: Sat Feb 23 15:23:50 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Sat Feb 23 17:12:15 2008 -0800

    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
       There's a similar debian bug that has been filed as well:
       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
    Signed-off-by: Paul Clements <[EMAIL PROTECTED]>
    Cc: Jens Axboe <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 drivers/block/nbd.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 018753c..b53fdb0 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)
                        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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