tree 77c9f33d65b78266560b3aa0bea1c7d16fb45b2e
parent 98262f2762f0067375f83824d81ea929e37e6bfe
author Shaohua Li <shaohua.li@intel.com> 1259841485 +0100
committer Jens Axboe <jens.axboe@oracle.com> 1259841485 +0100

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>