block cfq: select new workload if priority changed

If priority is changed, continuing to check workload_expires and service tree
count of the previous workload does not make sense. We should always choose
the workload with lowest key of new priority in such case.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5d0349d602f..9b186fd6bf4 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2101,6 +2101,7 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
         unsigned count;
         struct cfq_rb_root *st;
         unsigned group_slice;
+        enum wl_prio_t original_prio = cfqd->serving_prio;
 
         if (!cfqg) {
                 cfqd->serving_prio = IDLE_WORKLOAD;
@@ -2119,6 +2120,9 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
                 return;
         }
 
+        if (original_prio != cfqd->serving_prio)
+                goto new_workload;
+
         /*
          * For RT and BE, we have to choose also the type
          * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload
@@ -2133,6 +2137,7 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
         if (count && !time_after(jiffies, cfqd->workload_expires))
                 return;
 
+new_workload:
         /* otherwise select new workload type */
         cfqd->serving_type =
                 cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);