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authorJens Axboe <jens.axboe@oracle.com>2006-12-22 09:38:53 +0100
committerLinus Torvalds <torvalds@woody.osdl.org>2006-12-22 14:13:08 -0800
commit719d34027e1a186e46a3952e8a24bf91ecc33837 (patch)
treef0b9074069777c430045e7be803d8c5a2187ecc9
parentc2fda5fed81eea077363b285b66eafce20dfd45a (diff)
[PATCH] cfq-iosched: tighten allow merge criteria
The logic in cfq_allow_merge() wasn't clear enough - basically allow merging for the same queues only. Do a fast check for 'rq and bio both sync/async' before doing the cfqq hash lookup. This is verified to work with the fixed elv_try_merge() from commit bb4067e34159648d394943d5e2a011f838bff22f. Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--block/cfq-iosched.c21
1 files changed, 8 insertions, 13 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9fc5eafa6c0e..4b4217d9be78 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -577,25 +577,20 @@ static int cfq_allow_merge(request_queue_t *q, struct request *rq,
pid_t key;
/*
- * If bio is async or a write, always allow merge
+ * Disallow merge, if bio and rq aren't both sync or async
*/
- if (!bio_sync(bio) || rw == WRITE)
- return 1;
-
- /*
- * bio is sync. if request is not, disallow.
- */
- if (!rq_is_sync(rq))
+ if (!!bio_sync(bio) != !!rq_is_sync(rq))
return 0;
/*
- * Ok, both bio and request are sync. Allow merge if they are
- * from the same queue.
+ * Lookup the cfqq that this bio will be queued with. Allow
+ * merge only if rq is queued there.
*/
- key = cfq_queue_pid(current, rw, 1);
+ key = cfq_queue_pid(current, rw, bio_sync(bio));
cfqq = cfq_find_cfq_hash(cfqd, key, current->ioprio);
- if (cfqq != RQ_CFQQ(rq))
- return 0;
+
+ if (cfqq == RQ_CFQQ(rq))
+ return 1;
return 1;
}