cfq-iosched: make seek_mean converge more quickly

Right now, depending on the first sector to which a process issues I/O,
the seek time may start out way out of whack. So make sure we start
with 0 sectors in seek, instead of the offset of the first request
issued.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 0d3b70de3d8..0eb4aff9df6 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1908,7 +1908,9 @@ cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_io_context *cic,
         sector_t sdist;
         u64 total;
 
-        if (cic->last_request_pos < rq->sector)
+        if (!cic->last_request_pos)
+                sdist = 0;
+        else if (cic->last_request_pos < rq->sector)
                 sdist = rq->sector - cic->last_request_pos;
         else
                 sdist = cic->last_request_pos - rq->sector;