1 files changed, 24 insertions, 1 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 37abbfc68590..5352bdafbcf0 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -756,6 +756,15 @@ static void throtl_process_limit_change(struct throtl_data *td)
                         " riops=%u wiops=%u", tg->bps[READ], tg->bps[WRITE],
                         tg->iops[READ], tg->iops[WRITE]);
 
+                /*
+                 * Restart the slices for both READ and WRITES. It
+                 * might happen that a group's limit are dropped
+                 * suddenly and we don't want to account recently
+                 * dispatched IO with new low rate
+                 */
+                throtl_start_new_slice(td, tg, 0);
+                throtl_start_new_slice(td, tg, 1);
+
                 if (throtl_tg_on_rr(tg))
                         tg_update_disptime(td, tg);
         }
@@ -821,7 +830,8 @@ throtl_schedule_delayed_work(struct throtl_data *td, unsigned long delay)
 
         struct delayed_work *dwork = &td->throtl_work;
 
-        if (total_nr_queued(td) > 0) {
+        /* schedule work if limits changed even if no bio is queued */
+        if (total_nr_queued(td) > 0 || td->limits_changed) {
                 /*
                  * We might have a work scheduled to be executed in future.
                  * Cancel that and schedule a new one.
@@ -1002,6 +1012,19 @@ int blk_throtl_bio(struct request_queue *q, struct bio **biop)
         /* Bio is with-in rate limit of group */
         if (tg_may_dispatch(td, tg, bio, NULL)) {
                 throtl_charge_bio(tg, bio);
+
+                /*
+                 * We need to trim slice even when bios are not being queued
+                 * otherwise it might happen that a bio is not queued for
+                 * a long time and slice keeps on extending and trim is not
+                 * called for a long time. Now if limits are reduced suddenly
+                 * we take into account all the IO dispatched so far at new
+                 * low rate and * newly queued IO gets a really long dispatch
+                 * time.
+                 *
+                 * So keep on trimming slice even if bio is not queued.
+                 */
+                throtl_trim_slice(td, tg, rw);
                 goto out;
         }