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| author | Alan D. Brunelle <Alan.Brunelle@hp.com> | 2008-04-29 14:44:19 +0200 |
|---|---|---|
| committer | Jens Axboe <jens.axboe@oracle.com> | 2008-04-29 14:48:55 +0200 |
| commit | ac9fafa1243640349aa481adf473db283a695766 (patch) | |
| tree | 155c2371cca8971638d781269f39fa015bc6509c /block/elevator.c | |
| parent | d7e3c3249ef23b4617393c69fe464765b4ff1645 (diff) | |
| download | lwn-ac9fafa1243640349aa481adf473db283a695766.tar.gz lwn-ac9fafa1243640349aa481adf473db283a695766.zip | |
block: Skip I/O merges when disabled
The block I/O + elevator + I/O scheduler code spend a lot of time trying
to merge I/Os -- rightfully so under "normal" circumstances. However,
if one were to know that the incoming I/O stream was /very/ random in
nature, the cycles are wasted.
This patch adds a per-request_queue tunable that (when set) disables
merge attempts (beyond the simple one-hit cache check), thus freeing up
a non-trivial amount of CPU cycles.
Signed-off-by: Alan D. Brunelle <alan.brunelle@hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block/elevator.c')
| -rw-r--r-- | block/elevator.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/block/elevator.c b/block/elevator.c index 7253fa05db0a..ac5310ef8270 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -488,6 +488,9 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio) } } + if (blk_queue_nomerges(q)) + return ELEVATOR_NO_MERGE; + /* * See if our hash lookup can find a potential backmerge. */ |