blk-wbt: don't maintain inflight counts if disabled

axboe · axboe · commit c125311d96b1 · 2018-08-23T09:34:46.000-06:00
A previous commit removed the ability to have per-rq flags. We used those flags to maintain inflight counts. Since we don't have those anymore, we have to always maintain inflight counts, even if wbt is disabled. This is clearly suboptimal. Add a queue quiesce around changing the wbt latency settings from sysfs to work around this. With that, we can reliably put the enabled check in our bio_to_wbt_flags(), since we know the WBT_TRACKED flag will be consistent for the lifetime of the request. Fixes: c1c8038 ("block: remove external dependency on wbt_flags") Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
@@ -453,9 +453,26 @@ static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
 	else if (val >= 0)
 		val *= 1000ULL;
 
-	wbt_set_min_lat(q, val);
+	/*
+	 * Ensure that the queue is idled, in case the latency update
+	 * ends up either enabling or disabling wbt completely. We can't
+	 * have IO inflight if that happens.
+	 */
+	if (q->mq_ops) {
+		blk_mq_freeze_queue(q);
+		blk_mq_quiesce_queue(q);
+	} else
+		blk_queue_bypass_start(q);
 
+	wbt_set_min_lat(q, val);
 	wbt_update_limits(q);
+
+	if (q->mq_ops) {
+		blk_mq_unquiesce_queue(q);
+		blk_mq_unfreeze_queue(q);
+	} else
+		blk_queue_bypass_end(q);
+
 	return count;
 }
 
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
@@ -540,6 +540,9 @@ static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
 {
 	enum wbt_flags flags = 0;
 
+	if (!rwb_enabled(rwb))
+		return 0;
+
 	if (bio_op(bio) == REQ_OP_READ) {
 		flags = WBT_READ;
 	} else if (wbt_should_throttle(rwb, bio)) {

Original file line number	Diff line number	Diff line change
`@@ -540,6 +540,9 @@ static enum wbt_flags bio_to_wbt_flags(struct rq_wb rwb, struct bio bio)`
`540`	`540`	`{`
`541`	`541`	`enum wbt_flags flags = 0;`
`542`	`542`
	`543`	`+ if (!rwb_enabled(rwb))`
	`544`	`+ return 0;`
	`545`	`+`
`543`	`546`	`if (bio_op(bio) == REQ_OP_READ) {`
`544`	`547`	`flags = WBT_READ;`
`545`	`548`	`} else if (wbt_should_throttle(rwb, bio)) {`