path: root/block
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authorShaohua Li <shaohua.li@intel.com>2009-12-03 12:58:05 +0100
committerJens Axboe <jens.axboe@oracle.com>2009-12-03 12:58:05 +0100
commit474b18ccc264c472abeec50f48469b6477202699 (patch)
tree77c9f33d65b78266560b3aa0bea1c7d16fb45b2e /block
parent98262f2762f0067375f83824d81ea929e37e6bfe (diff)
cfq-iosched: no dispatch limit for single queue
Since commit 2f5cb7381b737e24c8046fd4aeab571fb71315f5, each queue can send up to 4 * 4 requests if only one queue exists. I wonder why we have such limit. Device supports tag can send more requests. For example, AHCI can send 31 requests. Test (direct aio randread) shows the limits reduce about 4% disk thoughput. On the other hand, since we send one request one time, if other queue pop when current is sending more than cfq_quantum requests, current queue will stop send requests soon after one request, so sounds there is no big latency. Signed-off-by: Shaohua Li <shaohua.li@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block')
1 files changed, 2 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 71446497d7b6..f5b59e18ebd3 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1618,9 +1618,9 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
return false;
- * Sole queue user, allow bigger slice
+ * Sole queue user, no limit
- max_dispatch *= 4;
+ max_dispatch = -1;