cfq-iosched: don't regard requests with long distance as close

seek_mean could be very big sometimes, using it as close criteria is meaningless
as this doen't improve any performance. So if it's big, let's fallback to
default value.

Reviewed-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 8df4fe58f4e7..918c7fd9aeb1 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1667,13 +1667,17 @@ static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
 #define CFQQ_SEEKY(cfqq)        ((cfqq)->seek_mean > CFQQ_SEEK_THR)
 
 static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
-                               struct request *rq)
+                               struct request *rq, bool for_preempt)
 {
         sector_t sdist = cfqq->seek_mean;
 
         if (!sample_valid(cfqq->seek_samples))
                 sdist = CFQQ_SEEK_THR;
 
+        /* if seek_mean is big, using it as close criteria is meaningless */
+        if (sdist > CFQQ_SEEK_THR && !for_preempt)
+                sdist = CFQQ_SEEK_THR;
+
         return cfq_dist_from_last(cfqd, rq) <= sdist;
 }
 
@@ -1701,7 +1705,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
          * will contain the closest sector.
          */
         __cfqq = rb_entry(parent, struct cfq_queue, p_node);
-        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
+        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false))
                 return __cfqq;
 
         if (blk_rq_pos(__cfqq->next_rq) < sector)
@@ -1712,7 +1716,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
                 return NULL;
 
         __cfqq = rb_entry(node, struct cfq_queue, p_node);
-        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
+        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false))
                 return __cfqq;
 
         return NULL;
@@ -3112,7 +3116,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
          * if this request is as-good as one we would expect from the
          * current cfqq, let it preempt
          */
-        if (cfq_rq_close(cfqd, cfqq, rq))
+        if (cfq_rq_close(cfqd, cfqq, rq, true))
                 return true;
 
         return false;