block: don't try to throttle split bio if iops limit isn't set

We need to throttle split bio in case of IOPS limit even though the
split bio has been marked as BIO_THROTTLED since block layer
accounts split bio actually.

If only throughput throttle is setup, no need to throttle any more
if BIO_THROTTLED is set since we have accounted & considered the
whole bio bytes already.

Add one flag of THROTL_TG_HAS_IOPS_LIMIT for serving this purpose.

Acked-by: Tejun Heo <[e-mail]>
Signed-off-by: Ming Lei <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

block/blk-throttle.c

···
 /* A workqueue to queue throttle related work */
 static struct workqueue_struct *kthrotld_workqueue;
 
-enum tg_state_flags {
-	THROTL_TG_PENDING	= 1 << 0,	/* on parent's pending tree */
-	THROTL_TG_WAS_EMPTY	= 1 << 1,	/* bio_lists[] became non-empty */
-};
-
 #define rb_entry_tg(node)	rb_entry((node), struct throtl_grp, rb_node)
 
 /* We measure latency for request size from <= 4k to >= 1M */
···
 	struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
 	struct throtl_data *td = tg->td;
 	int rw;
+	int has_iops_limit = 0;
 
-	for (rw = READ; rw <= WRITE; rw++)
+	for (rw = READ; rw <= WRITE; rw++) {
+		unsigned int iops_limit = tg_iops_limit(tg, rw);
+
 		tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
 			(td->limit_valid[td->limit_index] &&
 			 (tg_bps_limit(tg, rw) != U64_MAX ||
-			  tg_iops_limit(tg, rw) != UINT_MAX));
+			  iops_limit != UINT_MAX));
+
+		if (iops_limit != UINT_MAX)
+			has_iops_limit = 1;
+	}
+
+	if (has_iops_limit)
+		tg->flags |= THROTL_TG_HAS_IOPS_LIMIT;
+	else
+		tg->flags &= ~THROTL_TG_HAS_IOPS_LIMIT;
 }
 
 static void throtl_pd_online(struct blkg_policy_data *pd)

block/blk-throttle.h

···
 	struct timer_list	pending_timer;	/* fires on first_pending_disptime */
 };
 
+enum tg_state_flags {
+	THROTL_TG_PENDING	= 1 << 0,	/* on parent's pending tree */
+	THROTL_TG_WAS_EMPTY	= 1 << 1,	/* bio_lists[] became non-empty */
+	THROTL_TG_HAS_IOPS_LIMIT = 1 << 2,	/* tg has iops limit */
+};
+
 enum {
 	LIMIT_LOW,
 	LIMIT_MAX,
···
 static inline bool blk_throtl_bio(struct bio *bio)
 {
 	struct throtl_grp *tg = blkg_to_tg(bio->bi_blkg);
+
+	/* no need to throttle bps any more if the bio has been throttled */
+	if (bio_flagged(bio, BIO_THROTTLED) &&
+	    !(tg->flags & THROTL_TG_HAS_IOPS_LIMIT))
+		return false;
 
 	if (!tg->has_rules[bio_data_dir(bio)])
 		return false;