[V2,03/13] blk-throttle: add abstract to index data
diff mbox

Message ID 622874ae11d2159f4dae550fe309cbf1b4256a39.1456178093.git.shli@fb.com
State New
Headers show

Commit Message

Shaohua Li Feb. 22, 2016, 10:01 p.m. UTC
For throttle, we have separate data to track READ/WRITE IO. For weight
based throttle, we combine read/write bandwidth and check combined
bandwidth. Separate throttle doesn't work, because it's possible one
cgroup only does READ and the other only does WRITE. This patch adds
an abstract to index data. With it, later patch can easily do the
read/write combination track for weight based throttle.

In the future, we can introduce a sub queue for read and write for each
cgroup and give read more shares.

Signed-off-by: Shaohua Li <shli@fb.com>
---
 block/blk-throttle.c | 182 +++++++++++++++++++++++++++++----------------------
 1 file changed, 102 insertions(+), 80 deletions(-)

Patch
diff mbox

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index a4ae0a7..90f937f 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -207,6 +207,11 @@  static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
 		return container_of(sq, struct throtl_data, service_queue);
 }
 
+static inline int tg_data_index(struct throtl_grp *tg, bool rw)
+{
+	return rw;
+}
+
 /**
  * throtl_log - log debug message via blktrace
  * @sq: the service_queue being reported
@@ -338,7 +343,7 @@  static inline void io_cost_init(struct throtl_grp *tg)
 static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
 {
 	struct throtl_grp *tg;
-	int rw;
+	int i;
 
 	tg = kzalloc_node(sizeof(*tg), gfp, node);
 	if (!tg)
@@ -346,9 +351,9 @@  static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
 
 	throtl_service_queue_init(&tg->service_queue);
 
-	for (rw = READ; rw <= WRITE; rw++) {
-		throtl_qnode_init(&tg->qnode_on_self[rw], tg);
-		throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
+	for (i = READ; i <= WRITE; i++) {
+		throtl_qnode_init(&tg->qnode_on_self[i], tg);
+		throtl_qnode_init(&tg->qnode_on_parent[i], tg);
 	}
 
 	RB_CLEAR_NODE(&tg->rb_node);
@@ -384,9 +389,9 @@  static void throtl_pd_init(struct blkg_policy_data *pd)
 	tg->td = td;
 }
 
-static inline bool io_cost_has_limit(struct throtl_grp *tg, int rw)
+static inline bool io_cost_has_limit(struct throtl_grp *tg, int index)
 {
-	return tg->io_cost.bps[rw] != -1 || tg->io_cost.iops[rw] != -1;
+	return tg->io_cost.bps[index] != -1 || tg->io_cost.iops[index] != -1;
 }
 
 /*
@@ -397,11 +402,11 @@  static inline bool io_cost_has_limit(struct throtl_grp *tg, int rw)
 static void tg_update_has_rules(struct throtl_grp *tg)
 {
 	struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
-	int rw;
+	int i;
 
-	for (rw = READ; rw <= WRITE; rw++)
-		tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
-				    io_cost_has_limit(tg, rw);
+	for (i = READ; i <= WRITE; i++)
+		tg->has_rules[i] = (parent_tg && parent_tg->has_rules[i]) ||
+				    io_cost_has_limit(tg, i);
 }
 
 static void throtl_pd_online(struct blkg_policy_data *pd)
@@ -565,13 +570,15 @@  static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
 static inline void io_cost_start_new_slice(struct throtl_grp *tg,
 		bool rw)
 {
-	tg->io_cost.bytes_disp[rw] = 0;
-	tg->io_cost.io_disp[rw] = 0;
+	int index = tg_data_index(tg, rw);
+	tg->io_cost.bytes_disp[index] = 0;
+	tg->io_cost.io_disp[index] = 0;
 }
 
 static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
 		bool rw, unsigned long start)
 {
+	int index = tg_data_index(tg, rw);
 	io_cost_start_new_slice(tg, rw);
 
 	/*
@@ -580,47 +587,52 @@  static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
 	 * that bandwidth. Do try to make use of that bandwidth while giving
 	 * credit.
 	 */
-	if (time_after_eq(start, tg->slice_start[rw]))
-		tg->slice_start[rw] = start;
+	if (time_after_eq(start, tg->slice_start[index]))
+		tg->slice_start[index] = start;
 
-	tg->slice_end[rw] = jiffies + throtl_slice;
+	tg->slice_end[index] = jiffies + throtl_slice;
 	throtl_log(&tg->service_queue,
 		   "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
-		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
-		   tg->slice_end[rw], jiffies);
+		   rw == READ ? 'R' : 'W', tg->slice_start[index],
+		   tg->slice_end[index], jiffies);
 }
 
 static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
 {
+	int index = tg_data_index(tg, rw);
+
 	io_cost_start_new_slice(tg, rw);
-	tg->slice_start[rw] = jiffies;
-	tg->slice_end[rw] = jiffies + throtl_slice;
+	tg->slice_start[index] = jiffies;
+	tg->slice_end[index] = jiffies + throtl_slice;
 	throtl_log(&tg->service_queue,
 		   "[%c] new slice start=%lu end=%lu jiffies=%lu",
-		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
-		   tg->slice_end[rw], jiffies);
+		   rw == READ ? 'R' : 'W', tg->slice_start[index],
+		   tg->slice_end[index], jiffies);
 }
 
 static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
 					unsigned long jiffy_end)
 {
-	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+	int index = tg_data_index(tg, rw);
+	tg->slice_end[index] = roundup(jiffy_end, throtl_slice);
 }
 
 static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
 				       unsigned long jiffy_end)
 {
-	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+	int index = tg_data_index(tg, rw);
+	tg->slice_end[index] = roundup(jiffy_end, throtl_slice);
 	throtl_log(&tg->service_queue,
 		   "[%c] extend slice start=%lu end=%lu jiffies=%lu",
-		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
-		   tg->slice_end[rw], jiffies);
+		   rw == READ ? 'R' : 'W', tg->slice_start[index],
+		   tg->slice_end[index], jiffies);
 }
 
 /* Determine if previously allocated or extended slice is complete or not */
 static bool throtl_slice_used(struct throtl_grp *tg, bool rw)
 {
-	if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
+	int index = tg_data_index(tg, rw);
+	if (time_in_range(jiffies, tg->slice_start[index], tg->slice_end[index]))
 		return false;
 
 	return 1;
@@ -631,25 +643,26 @@  static inline bool io_cost_trim_slice(struct throtl_grp *tg, bool rw,
 {
 	unsigned long io_trim;
 	u64 bytes_trim, tmp;
+	int index = tg_data_index(tg, rw);
 
-	tmp = tg->io_cost.bps[rw] * throtl_slice * nr_slices;
+	tmp = tg->io_cost.bps[index] * throtl_slice * nr_slices;
 	do_div(tmp, HZ);
 	bytes_trim = tmp;
 
-	io_trim = (tg->io_cost.iops[rw] * throtl_slice * nr_slices) / HZ;
+	io_trim = (tg->io_cost.iops[index] * throtl_slice * nr_slices) / HZ;
 
 	if (!bytes_trim && !io_trim)
 		return false;
 
-	if (tg->io_cost.bytes_disp[rw] >= bytes_trim)
-		tg->io_cost.bytes_disp[rw] -= bytes_trim;
+	if (tg->io_cost.bytes_disp[index] >= bytes_trim)
+		tg->io_cost.bytes_disp[index] -= bytes_trim;
 	else
-		tg->io_cost.bytes_disp[rw] = 0;
+		tg->io_cost.bytes_disp[index] = 0;
 
-	if (tg->io_cost.io_disp[rw] >= io_trim)
-		tg->io_cost.io_disp[rw] -= io_trim;
+	if (tg->io_cost.io_disp[index] >= io_trim)
+		tg->io_cost.io_disp[index] -= io_trim;
 	else
-		tg->io_cost.io_disp[rw] = 0;
+		tg->io_cost.io_disp[index] = 0;
 
 	return true;
 }
@@ -658,8 +671,9 @@  static inline bool io_cost_trim_slice(struct throtl_grp *tg, bool rw,
 static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 {
 	unsigned long nr_slices, time_elapsed;
+	int index = tg_data_index(tg, rw);
 
-	BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
+	BUG_ON(time_before(tg->slice_end[index], tg->slice_start[index]));
 
 	/*
 	 * If bps are unlimited (-1), then time slice don't get
@@ -679,7 +693,7 @@  static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 
 	throtl_set_slice_end(tg, rw, jiffies + throtl_slice);
 
-	time_elapsed = jiffies - tg->slice_start[rw];
+	time_elapsed = jiffies - tg->slice_start[index];
 
 	nr_slices = time_elapsed / throtl_slice;
 
@@ -688,23 +702,24 @@  static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 
 	if (!io_cost_trim_slice(tg, rw, nr_slices))
 		return;
-	tg->slice_start[rw] += nr_slices * throtl_slice;
+	tg->slice_start[index] += nr_slices * throtl_slice;
 
 	throtl_log(&tg->service_queue,
 		   "[%c] trim slice nr=%lu start=%lu end=%lu jiffies=%lu",
 		   rw == READ ? 'R' : 'W', nr_slices,
-		   tg->slice_start[rw], tg->slice_end[rw], jiffies);
+		   tg->slice_start[index], tg->slice_end[index], jiffies);
 }
 
 static bool io_cost_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
 				  unsigned long *wait)
 {
 	bool rw = bio_data_dir(bio);
+	int index = tg_data_index(tg, rw);
 	unsigned int io_allowed;
 	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
 	u64 tmp;
 
-	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
+	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[index];
 
 	/* Slice has just started. Consider one slice interval */
 	if (!jiffy_elapsed)
@@ -719,7 +734,7 @@  static bool io_cost_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
 	 * have been trimmed.
 	 */
 
-	tmp = (u64)tg->io_cost.iops[rw] * jiffy_elapsed_rnd;
+	tmp = (u64)tg->io_cost.iops[index] * jiffy_elapsed_rnd;
 	do_div(tmp, HZ);
 
 	if (tmp > UINT_MAX)
@@ -727,15 +742,15 @@  static bool io_cost_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
 	else
 		io_allowed = tmp;
 
-	if (tg->io_cost.io_disp[rw] + 1 <= io_allowed) {
+	if (tg->io_cost.io_disp[index] + 1 <= io_allowed) {
 		if (wait)
 			*wait = 0;
 		return true;
 	}
 
 	/* Calc approx time to dispatch */
-	jiffy_wait = ((tg->io_cost.io_disp[rw] + 1) * HZ) /
-		tg->io_cost.iops[rw] + 1;
+	jiffy_wait = ((tg->io_cost.io_disp[index] + 1) * HZ) /
+		tg->io_cost.iops[index] + 1;
 
 	if (jiffy_wait > jiffy_elapsed)
 		jiffy_wait = jiffy_wait - jiffy_elapsed;
@@ -751,10 +766,11 @@  static bool io_cost_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 				 unsigned long *wait)
 {
 	bool rw = bio_data_dir(bio);
+	int index = tg_data_index(tg, rw);
 	u64 bytes_allowed, extra_bytes, tmp;
 	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
 
-	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
+	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[index];
 
 	/* Slice has just started. Consider one slice interval */
 	if (!jiffy_elapsed)
@@ -762,11 +778,11 @@  static bool io_cost_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 
 	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
 
-	tmp = tg->io_cost.bps[rw] * jiffy_elapsed_rnd;
+	tmp = tg->io_cost.bps[index] * jiffy_elapsed_rnd;
 	do_div(tmp, HZ);
 	bytes_allowed = tmp;
 
-	if (tg->io_cost.bytes_disp[rw] + bio->bi_iter.bi_size <=
+	if (tg->io_cost.bytes_disp[index] + bio->bi_iter.bi_size <=
 	    bytes_allowed) {
 		if (wait)
 			*wait = 0;
@@ -774,9 +790,9 @@  static bool io_cost_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 	}
 
 	/* Calc approx time to dispatch */
-	extra_bytes = tg->io_cost.bytes_disp[rw] +
+	extra_bytes = tg->io_cost.bytes_disp[index] +
 		bio->bi_iter.bi_size - bytes_allowed;
-	jiffy_wait = div64_u64(extra_bytes * HZ, tg->io_cost.bps[rw]);
+	jiffy_wait = div64_u64(extra_bytes * HZ, tg->io_cost.bps[index]);
 
 	if (!jiffy_wait)
 		jiffy_wait = 1;
@@ -813,6 +829,7 @@  static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 			    unsigned long *wait)
 {
 	bool rw = bio_data_dir(bio);
+	int index = tg_data_index(tg, rw);
 	unsigned long max_wait = 0;
 
 	/*
@@ -821,11 +838,11 @@  static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 	 * this function with a different bio if there are other bios
 	 * queued.
 	 */
-	BUG_ON(tg->service_queue.nr_queued[rw] &&
-	       bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
+	BUG_ON(tg->service_queue.nr_queued[index] &&
+	       bio != throtl_peek_queued(&tg->service_queue.queued[index]));
 
 	/* If tg->bps = -1, then BW is unlimited */
-	if (!io_cost_has_limit(tg, rw)) {
+	if (!io_cost_has_limit(tg, index)) {
 		if (wait)
 			*wait = 0;
 		return true;
@@ -839,7 +856,7 @@  static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 	if (throtl_slice_used(tg, rw))
 		throtl_start_new_slice(tg, rw);
 	else {
-		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
+		if (time_before(tg->slice_end[index], jiffies + throtl_slice))
 			throtl_extend_slice(tg, rw, jiffies + throtl_slice);
 	}
 
@@ -852,7 +869,7 @@  static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 	if (wait)
 		*wait = max_wait;
 
-	if (time_before(tg->slice_end[rw], jiffies + max_wait))
+	if (time_before(tg->slice_end[index], jiffies + max_wait))
 		throtl_extend_slice(tg, rw, jiffies + max_wait);
 
 	return false;
@@ -861,10 +878,11 @@  static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 static inline void io_cost_charge_bio(struct throtl_grp *tg, struct bio *bio)
 {
 	bool rw = bio_data_dir(bio);
+	int index = tg_data_index(tg, rw);
 
 	/* Charge the bio to the group */
-	tg->io_cost.bytes_disp[rw] += bio->bi_iter.bi_size;
-	tg->io_cost.io_disp[rw]++;
+	tg->io_cost.bytes_disp[index] += bio->bi_iter.bi_size;
+	tg->io_cost.io_disp[index]++;
 }
 
 static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
@@ -894,9 +912,10 @@  static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
 {
 	struct throtl_service_queue *sq = &tg->service_queue;
 	bool rw = bio_data_dir(bio);
+	int index = tg_data_index(tg, rw);
 
 	if (!qn)
-		qn = &tg->qnode_on_self[rw];
+		qn = &tg->qnode_on_self[index];
 
 	/*
 	 * If @tg doesn't currently have any bios queued in the same
@@ -904,12 +923,12 @@  static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
 	 * dispatched.  Mark that @tg was empty.  This is automatically
 	 * cleaered on the next tg_update_disptime().
 	 */
-	if (!sq->nr_queued[rw])
+	if (!sq->nr_queued[index])
 		tg->flags |= THROTL_TG_WAS_EMPTY;
 
-	throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
+	throtl_qnode_add_bio(bio, qn, &sq->queued[index]);
 
-	sq->nr_queued[rw]++;
+	sq->nr_queued[index]++;
 	throtl_enqueue_tg(tg);
 }
 
@@ -940,9 +959,10 @@  static void tg_update_disptime(struct throtl_grp *tg)
 static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
 					struct throtl_grp *parent_tg, bool rw)
 {
+	int index = tg_data_index(child_tg, rw);
 	if (throtl_slice_used(parent_tg, rw)) {
 		throtl_start_new_slice_with_credit(parent_tg, rw,
-				child_tg->slice_start[rw]);
+				child_tg->slice_start[index]);
 	}
 
 }
@@ -954,6 +974,7 @@  static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
 	struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
 	struct throtl_grp *tg_to_put = NULL;
 	struct bio *bio;
+	int index = tg_data_index(tg, rw);
 
 	/*
 	 * @bio is being transferred from @tg to @parent_sq.  Popping a bio
@@ -961,8 +982,8 @@  static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
 	 * getting released prematurely.  Remember the tg to put and put it
 	 * after @bio is transferred to @parent_sq.
 	 */
-	bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
-	sq->nr_queued[rw]--;
+	bio = throtl_pop_queued(&sq->queued[index], &tg_to_put);
+	sq->nr_queued[index]--;
 
 	throtl_charge_bio(tg, bio);
 
@@ -974,13 +995,13 @@  static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
 	 * responsible for issuing these bios.
 	 */
 	if (parent_tg) {
-		throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
+		throtl_add_bio_tg(bio, &tg->qnode_on_parent[index], parent_tg);
 		start_parent_slice_with_credit(tg, parent_tg, rw);
 	} else {
-		throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
-				     &parent_sq->queued[rw]);
-		BUG_ON(tg->td->nr_queued[rw] <= 0);
-		tg->td->nr_queued[rw]--;
+		throtl_qnode_add_bio(bio, &tg->qnode_on_parent[index],
+				     &parent_sq->queued[index]);
+		BUG_ON(tg->td->nr_queued[index] <= 0);
+		tg->td->nr_queued[index]--;
 	}
 
 	throtl_trim_slice(tg, rw);
@@ -1139,13 +1160,13 @@  static void blk_throtl_dispatch_work_fn(struct work_struct *work)
 	struct bio_list bio_list_on_stack;
 	struct bio *bio;
 	struct blk_plug plug;
-	int rw;
+	int i;
 
 	bio_list_init(&bio_list_on_stack);
 
 	spin_lock_irq(q->queue_lock);
-	for (rw = READ; rw <= WRITE; rw++)
-		while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
+	for (i = READ; i <= WRITE; i++)
+		while ((bio = throtl_pop_queued(&td_sq->queued[i], NULL)))
 			bio_list_add(&bio_list_on_stack, bio);
 	spin_unlock_irq(q->queue_lock);
 
@@ -1453,12 +1474,13 @@  bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
 	struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
 	struct throtl_service_queue *sq;
 	bool rw = bio_data_dir(bio);
+	int index = tg_data_index(tg, rw);
 	bool throttled = false;
 
 	WARN_ON_ONCE(!rcu_read_lock_held());
 
 	/* see throtl_charge_bio() */
-	if ((bio->bi_rw & REQ_THROTTLED) || !tg->has_rules[rw])
+	if ((bio->bi_rw & REQ_THROTTLED) || !tg->has_rules[index])
 		goto out;
 
 	spin_lock_irq(q->queue_lock);
@@ -1470,7 +1492,7 @@  bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
 
 	while (true) {
 		/* throtl is FIFO - if bios are already queued, should queue */
-		if (sq->nr_queued[rw])
+		if (sq->nr_queued[index])
 			break;
 
 		/* if above limits, break to queue */
@@ -1498,7 +1520,7 @@  bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
 		 * Climb up the ladder.  If we''re already at the top, it
 		 * can be executed directly.
 		 */
-		qn = &tg->qnode_on_parent[rw];
+		qn = &tg->qnode_on_parent[index];
 		sq = sq->parent_sq;
 		tg = sq_to_tg(sq);
 		if (!tg)
@@ -1508,13 +1530,13 @@  bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
 	/* out-of-limit, queue to @tg */
 	throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
 		   rw == READ ? 'R' : 'W',
-		   tg->io_cost.bytes_disp[rw], bio->bi_iter.bi_size,
-		   tg->io_cost.bps[rw], tg->io_cost.io_disp[rw],
-		   tg->io_cost.iops[rw],
+		   tg->io_cost.bytes_disp[index], bio->bi_iter.bi_size,
+		   tg->io_cost.bps[index], tg->io_cost.io_disp[index],
+		   tg->io_cost.iops[index],
 		   sq->nr_queued[READ], sq->nr_queued[WRITE]);
 
 	bio_associate_current(bio);
-	tg->td->nr_queued[rw]++;
+	tg->td->nr_queued[index]++;
 	throtl_add_bio_tg(bio, qn, tg);
 	throttled = true;
 
@@ -1577,7 +1599,7 @@  void blk_throtl_drain(struct request_queue *q)
 	struct blkcg_gq *blkg;
 	struct cgroup_subsys_state *pos_css;
 	struct bio *bio;
-	int rw;
+	int i;
 
 	queue_lockdep_assert_held(q);
 	rcu_read_lock();
@@ -1598,8 +1620,8 @@  void blk_throtl_drain(struct request_queue *q)
 	spin_unlock_irq(q->queue_lock);
 
 	/* all bios now should be in td->service_queue, issue them */
-	for (rw = READ; rw <= WRITE; rw++)
-		while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
+	for (i = READ; i <= WRITE; i++)
+		while ((bio = throtl_pop_queued(&td->service_queue.queued[i],
 						NULL)))
 			generic_make_request(bio);