diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index d083f7704082..4d2bda812d9b 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1546,19 +1546,39 @@ skip_surplus_transfers:
 	if (rq_wait_pct > RQ_WAIT_BUSY_PCT ||
 	    missed_ppm[READ] > ppm_rthr ||
 	    missed_ppm[WRITE] > ppm_wthr) {
+		/* clearly missing QoS targets, slow down vrate */
 		ioc->busy_level = max(ioc->busy_level, 0);
 		ioc->busy_level++;
 	} else if (rq_wait_pct <= RQ_WAIT_BUSY_PCT * UNBUSY_THR_PCT / 100 &&
 		   missed_ppm[READ] <= ppm_rthr * UNBUSY_THR_PCT / 100 &&
 		   missed_ppm[WRITE] <= ppm_wthr * UNBUSY_THR_PCT / 100) {
-		/* take action iff there is contention */
-		if (nr_shortages && !nr_lagging) {
+		/* QoS targets are being met with >25% margin */
+		if (nr_shortages) {
+			/*
+			 * We're throttling while the device has spare
+			 * capacity.  If vrate was being slowed down, stop.
+			 */
 			ioc->busy_level = min(ioc->busy_level, 0);
-			/* redistribute surpluses first */
-			if (!nr_surpluses)
+
+			/*
+			 * If there are IOs spanning multiple periods, wait
+			 * them out before pushing the device harder.  If
+			 * there are surpluses, let redistribution work it
+			 * out first.
+			 */
+			if (!nr_lagging && !nr_surpluses)
 				ioc->busy_level--;
+		} else {
+			/*
+			 * Nobody is being throttled and the users aren't
+			 * issuing enough IOs to saturate the device.  We
+			 * simply don't know how close the device is to
+			 * saturation.  Coast.
+			 */
+			ioc->busy_level = 0;
 		}
 	} else {
+		/* inside the hysterisis margin, we're good */
 		ioc->busy_level = 0;
 	}