[PATCH V6 4/8] block, bfq: turn bfqq_data into an array in bfq_io_cq

[Paolo Valente]

When a bfq_queue Q is merged with another queue, several pieces of
information are saved about Q. These pieces are stored in the
bfqq_data field in the bfq_io_cq data structure of the process
associated with Q.

Yet, with a multi-actuator drive, a process may get associated with
multiple bfq_queues: one queue for each of the N actuators. Each of
these queues may undergo a merge. So, the bfq_io_cq data structure
must be able to accommodate the above information for N queues.

This commit solves this problem by turning the bfqq_data scalar field
into an array of N elements (and by changing code so as to handle
this array).

This solution is written under the assumption that bfq_queues
associated with different actuators cannot be cross-merged. This
assumption holds naturally with basic queue merging: the latter is
triggered by spatial locality, and sectors for different actuators are
not close to each other. As for stable cross-merging, the assumption
here is that it is disabled.

Signed-off-by: Gabriele Felici <felicigb@xxxxxxxxx>
Signed-off-by: Gianmarco Lusvardi <glusvardi@xxxxxxxxxx>
Signed-off-by: Giulio Barabino <giuliobarabino99@xxxxxxxxx>
Signed-off-by: Emiliano Maccaferri <inbox@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
---
 block/bfq-iosched.c | 72 ++++++++++++++++++++++++---------------------
 block/bfq-iosched.h | 12 +++++---
 2 files changed, 47 insertions(+), 37 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 01528182c0c5..f44bac054aaf 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -404,7 +404,7 @@ void bic_set_bfqq(struct bfq_io_cq *bic,
 	 * we cancel the stable merge if
 	 * bic->stable_merge_bfqq == bfqq.
 	 */
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
+	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[actuator_idx];
 	bic->bfqq[is_sync][actuator_idx] = bfqq;
 
 	if (bfqq && bfqq_data->stable_merge_bfqq == bfqq) {
@@ -1175,9 +1175,10 @@ static void
 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
 		      struct bfq_io_cq *bic, bool bfq_already_existing)
 {
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
 	unsigned int old_wr_coeff = 1;
 	bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
+	unsigned int a_idx = bfqq->actuator_idx;
+	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx];
 
 	if (bfqq_data->saved_has_short_ttime)
 		bfq_mark_bfqq_has_short_ttime(bfqq);
@@ -1827,6 +1828,16 @@ static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
 	return bfqq_weight > in_serv_weight;
 }
 
+/* get the index of the actuator that will serve bio */
+static unsigned int bfq_actuator_index(struct bfq_data *bfqd, struct bio *bio)
+{
+	/*
+	 * Multi-actuator support not complete yet, so always return 0
+	 * for the moment.
+	 */
+	return 0;
+}
+
 static bool bfq_better_to_idle(struct bfq_queue *bfqq);
 
 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
@@ -1881,7 +1892,9 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
 	wr_or_deserves_wr = bfqd->low_latency &&
 		(bfqq->wr_coeff > 1 ||
 		 (bfq_bfqq_sync(bfqq) &&
-		  (bfqq->bic || RQ_BIC(rq)->bfqq_data.stably_merged) &&
+		  (bfqq->bic ||
+		   RQ_BIC(rq)->bfqq_data[bfq_actuator_index(bfqd, rq->bio)]
+		   .stably_merged) &&
 		   (*interactive || soft_rt)));
 
 	/*
@@ -2469,16 +2482,6 @@ static void bfq_remove_request(struct request_queue *q,
 
 }
 
-/* get the index of the actuator that will serve bio */
-static unsigned int bfq_actuator_index(struct bfq_data *bfqd, struct bio *bio)
-{
-	/*
-	 * Multi-actuator support not complete yet, so always return 0
-	 * for the moment.
-	 */
-	return 0;
-}
-
 static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
 		unsigned int nr_segs)
 {
@@ -2905,7 +2908,8 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		     void *io_struct, bool request, struct bfq_io_cq *bic)
 {
 	struct bfq_queue *in_service_bfqq, *new_bfqq;
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
+	unsigned int a_idx = bfqq->actuator_idx;
+	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx];
 
 	/* if a merge has already been setup, then proceed with that first */
 	if (bfqq->new_bfqq)
@@ -2952,8 +2956,9 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 				if (new_bfqq) {
 					bfqq_data->stably_merged = true;
 					if (new_bfqq->bic)
-						new_bfqq->bic->bfqq_data.stably_merged =
-							true;
+						new_bfqq->bic->bfqq_data
+							[new_bfqq->actuator_idx]
+							.stably_merged = true;
 				}
 				return new_bfqq;
 			} else
@@ -3052,7 +3057,9 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
 {
 	struct bfq_io_cq *bic = bfqq->bic;
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
+	/* State must be saved for the right queue index. */
+	unsigned int a_idx = bfqq->actuator_idx;
+	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx];
 
 	/*
 	 * If !bfqq->bic, the queue is already shared or its requests
@@ -3063,7 +3070,7 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
 		return;
 
 	bfqq_data->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
-	bfqq_data->saved_inject_limit = bfqq->inject_limit;
+	bfqq_data->saved_inject_limit =	bfqq->inject_limit;
 	bfqq_data->saved_decrease_time_jif = bfqq->decrease_time_jif;
 
 	bfqq_data->saved_weight = bfqq->entity.orig_weight;
@@ -5425,7 +5432,7 @@ static void bfq_exit_icq(struct io_cq *icq)
 	unsigned long flags;
 	unsigned int act_idx;
 	unsigned int num_actuators;
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
+	struct bfq_iocq_bfqq_data *bfqq_data = bic->bfqq_data;
 
 	/*
 	 * bfqd is NULL if scheduler already exited, and in that case
@@ -5445,10 +5452,10 @@ static void bfq_exit_icq(struct io_cq *icq)
 		num_actuators = BFQ_MAX_ACTUATORS;
 	}
 
-	if (bfqq_data->stable_merge_bfqq)
-		bfq_put_stable_ref(bfqq_data->stable_merge_bfqq);
-
 	for (act_idx = 0; act_idx < num_actuators; act_idx++) {
+		if (bfqq_data[act_idx].stable_merge_bfqq)
+			bfq_put_stable_ref(bfqq_data[act_idx].stable_merge_bfqq);
+
 		bfq_exit_icq_bfqq(bic, true, act_idx);
 		bfq_exit_icq_bfqq(bic, false, act_idx);
 	}
@@ -5635,16 +5642,16 @@ bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 			  struct bfq_io_cq *bic,
 			  struct bfq_queue *last_bfqq_created)
 {
+	unsigned int a_idx = last_bfqq_created->actuator_idx;
 	struct bfq_queue *new_bfqq =
 		bfq_setup_merge(bfqq, last_bfqq_created);
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
 
 	if (!new_bfqq)
 		return bfqq;
 
 	if (new_bfqq->bic)
-		new_bfqq->bic->bfqq_data.stably_merged = true;
-	bfqq_data->stably_merged = true;
+		new_bfqq->bic->bfqq_data[a_idx].stably_merged = true;
+	bic->bfqq_data[a_idx].stably_merged = true;
 
 	/*
 	 * Reusing merge functions. This implies that
@@ -5713,7 +5720,6 @@ static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
 		&bfqd->last_bfqq_created;
 
 	struct bfq_queue *last_bfqq_created = *source_bfqq;
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
 
 	/*
 	 * If last_bfqq_created has not been set yet, then init it. If
@@ -5775,7 +5781,8 @@ static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
 			/*
 			 * Record the bfqq to merge to.
 			 */
-			bfqq_data->stable_merge_bfqq = last_bfqq_created;
+			bic->bfqq_data[last_bfqq_created->actuator_idx].stable_merge_bfqq =
+				last_bfqq_created;
 		}
 	}
 
@@ -6696,7 +6703,7 @@ static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
 {
 	unsigned int act_idx = bfq_actuator_index(bfqd, bio);
 	struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync, act_idx);
-	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data;
+	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[act_idx];
 
 	if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
 		return bfqq;
@@ -6804,7 +6811,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
 	struct bfq_queue *bfqq;
 	bool new_queue = false;
 	bool bfqq_already_existing = false, split = false;
-	struct bfq_iocq_bfqq_data *bfqq_data;
+	unsigned int a_idx = bfq_actuator_index(bfqd, bio);
 
 	if (unlikely(!rq->elv.icq))
 		return NULL;
@@ -6828,17 +6835,16 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
 	bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
 					 &new_queue);
 
-	bfqq_data = &bic->bfqq_data;
-
 	if (likely(!new_queue)) {
 		/* If the queue was seeky for too long, break it apart. */
 		if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
-			!bfqq_data->stably_merged) {
+			!bic->bfqq_data[a_idx].stably_merged) {
 			struct bfq_queue *old_bfqq = bfqq;
 
 			/* Update bic before losing reference to bfqq */
 			if (bfq_bfqq_in_large_burst(bfqq))
-				bfqq_data->saved_in_large_burst = true;
+				bic->bfqq_data[a_idx].saved_in_large_burst =
+					true;
 
 			bfqq = bfq_split_bfqq(bic, bfqq);
 			split = true;
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index f2e8ab91951c..e27897d66a0f 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -416,7 +416,7 @@ struct bfq_queue {
 struct bfq_iocq_bfqq_data {
 	/*
 	 * Snapshot of the has_short_time flag before merging; taken
-	 * to remember its value while the queue is merged, so as to
+	 * to remember its values while the queue is merged, so as to
 	 * be able to restore it in case of split.
 	 */
 	bool saved_has_short_ttime;
@@ -430,7 +430,7 @@ struct bfq_iocq_bfqq_data {
 	u64 saved_tot_idle_time;
 
 	/*
-	 * Same purpose as the previous fields for the value of the
+	 * Same purpose as the previous fields for the values of the
 	 * field keeping the queue's belonging to a large burst
 	 */
 	bool saved_in_large_burst;
@@ -493,8 +493,12 @@ struct bfq_io_cq {
 	uint64_t blkcg_serial_nr; /* the current blkcg serial */
 #endif
 
-	/* persistent data for associated synchronous process queue */
-	struct bfq_iocq_bfqq_data bfqq_data;
+	/*
+	 * Persistent data for associated synchronous process queues
+	 * (one queue per actuator, see field bfqq above). In
+	 * particular, each of these queues may undergo a merge.
+	 */
+	struct bfq_iocq_bfqq_data bfqq_data[BFQ_MAX_ACTUATORS];
 
 	unsigned int requests;	/* Number of requests this process has in flight */
 };
-- 
2.20.1