[PATCH V4 7/8] block: don't try to throttle split bio if iops limit isn't set

[Ming Lei <ming.lei@xxxxxxxxxx>]

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 <tj@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 block/blk-throttle.c | 21 ++++++++++++++-------
 block/blk-throttle.h | 11 +++++++++++
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index c7aa26d52e84..ec72eced24d2 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -41,11 +41,6 @@
 /* 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 */
@@ -425,12 +420,24 @@ static void tg_update_has_rules(struct throtl_grp *tg)
 	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++) {
+		unsigned int iops_limit = tg_iops_limit(tg, rw);
 
-	for (rw = READ; rw <= WRITE; 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)
diff --git a/block/blk-throttle.h b/block/blk-throttle.h
index cb43f4417d6e..c996a15f290e 100644
--- a/block/blk-throttle.h
+++ b/block/blk-throttle.h
@@ -52,6 +52,12 @@ struct throtl_service_queue {
 	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,
@@ -170,6 +176,11 @@ 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;
 
-- 
2.31.1