Merge branch 'for-7.1/block' into for-next

* for-7.1/block:
  blk-iocost: fix busy_level reset when no IOs complete

Author: axboe

block/blk-iocost.c

@@ -1596,7 +1596,8 @@ static enum hrtimer_restart iocg_waitq_timer_fn(struct hrtimer *timer)
 	return HRTIMER_NORESTART;
 }
 
-static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p)
+static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p,
+			 u32 *nr_done)
 {
 	u32 nr_met[2] = { };
 	u32 nr_missed[2] = { };
@@ -1633,6 +1634,8 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
 
 	*rq_wait_pct_p = div64_u64(rq_wait_ns * 100,
 				   ioc->period_us * NSEC_PER_USEC);
+
+	*nr_done = nr_met[READ] + nr_met[WRITE] + nr_missed[READ] + nr_missed[WRITE];
 }
 
 /* was iocg idle this period? */
@@ -2250,12 +2253,12 @@ static void ioc_timer_fn(struct timer_list *timer)
 	u64 usage_us_sum = 0;
 	u32 ppm_rthr;
 	u32 ppm_wthr;
-	u32 missed_ppm[2], rq_wait_pct;
+	u32 missed_ppm[2], rq_wait_pct, nr_done;
 	u64 period_vtime;
 	int prev_busy_level;
 
 	/* how were the latencies during the period? */
-	ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct);
+	ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct, &nr_done);
 
 	/* take care of active iocgs */
 	spin_lock_irq(&ioc->lock);
@@ -2397,9 +2400,17 @@ static void ioc_timer_fn(struct timer_list *timer)
 	 * and should increase vtime rate.
 	 */
 	prev_busy_level = ioc->busy_level;
-	if (rq_wait_pct > RQ_WAIT_BUSY_PCT ||
-	    missed_ppm[READ] > ppm_rthr ||
-	    missed_ppm[WRITE] > ppm_wthr) {
+	if (!nr_done && nr_lagging) {
+		/*
+		 * When there are lagging IOs but no completions, we don't
+		 * know if the IO latency will meet the QoS targets. The
+		 * disk might be saturated or not. We should not reset
+		 * busy_level to 0 (which would prevent vrate from scaling
+		 * up or down), but rather to keep it unchanged.
+		 */
+	} else 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++;