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>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5d0349d..9b186fd 100644 (file)
--- 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);