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From:   Paolo Valente <paolo.valente@linaro.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        jack@suse.cz, andrea.righi@canonical.com, glen.valante@linaro.org,
        arie.vanderhoeven@seagate.com, rory.c.chen@seagate.com,
        Paolo Valente <paolo.valente@linaro.org>,
        Gabriele Felici <felicigb@gmail.com>
Subject: [PATCH V3 3/8] block, bfq: turn scalar fields into arrays in bfq_io_cq
Date:   Tue,  4 Oct 2022 11:40:05 +0200
Message-Id: <20221004094010.80090-4-paolo.valente@linaro.org>
In-Reply-To: <20221004094010.80090-1-paolo.valente@linaro.org>
References: <20221004094010.80090-1-paolo.valente@linaro.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When a bfq_queue Q is merged with another queue, several pieces of
information are saved about Q. These pieces are stored in the
bfq_io_cq data structure of the process associated with Q. In
particular, each such piece is represented by a scalar field in
bfq_io_cq.

Yet, with a multi-actuator drive, a process gets 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 each scalar field into an
array of N elements (and by changing code so as to handle these
arrays).

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@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
 block/bfq-iosched.c | 139 ++++++++++++++++++++++++--------------------
 block/bfq-iosched.h |  52 ++++++++++-------
 2 files changed, 105 insertions(+), 86 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 2a75009c1c06..dede0e948836 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -406,7 +406,7 @@ void bic_set_bfqq(struct bfq_io_cq *bic,
 	 */
 	bic->bfqq[is_sync][actuator_idx] = bfqq;
 
-	if (bfqq && bic->stable_merge_bfqq == bfqq) {
+	if (bfqq && bic->stable_merge_bfqq[actuator_idx] == bfqq) {
 		/*
 		 * Actually, these same instructions are executed also
 		 * in bfq_setup_cooperator, in case of abort or actual
@@ -415,9 +415,9 @@ void bic_set_bfqq(struct bfq_io_cq *bic,
 		 * did so, we would nest even more complexity in this
 		 * function.
 		 */
-		bfq_put_stable_ref(bic->stable_merge_bfqq);
+		bfq_put_stable_ref(bic->stable_merge_bfqq[actuator_idx]);
 
-		bic->stable_merge_bfqq = NULL;
+		bic->stable_merge_bfqq[actuator_idx] = NULL;
 	}
 }
 
@@ -1176,36 +1176,38 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
 {
 	unsigned int old_wr_coeff = 1;
 	bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
+	unsigned int a_idx = bfqq->actuator_idx;
 
-	if (bic->saved_has_short_ttime)
+	if (bic->saved_has_short_ttime[a_idx])
 		bfq_mark_bfqq_has_short_ttime(bfqq);
 	else
 		bfq_clear_bfqq_has_short_ttime(bfqq);
 
-	if (bic->saved_IO_bound)
+	if (bic->saved_IO_bound[a_idx])
 		bfq_mark_bfqq_IO_bound(bfqq);
 	else
 		bfq_clear_bfqq_IO_bound(bfqq);
 
-	bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns;
-	bfqq->inject_limit = bic->saved_inject_limit;
-	bfqq->decrease_time_jif = bic->saved_decrease_time_jif;
+	bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns[a_idx];
+	bfqq->inject_limit = bic->saved_inject_limit[a_idx];
+	bfqq->decrease_time_jif = bic->saved_decrease_time_jif[a_idx];
 
-	bfqq->entity.new_weight = bic->saved_weight;
-	bfqq->ttime = bic->saved_ttime;
-	bfqq->io_start_time = bic->saved_io_start_time;
-	bfqq->tot_idle_time = bic->saved_tot_idle_time;
+	bfqq->entity.new_weight = bic->saved_weight[a_idx];
+	bfqq->ttime = bic->saved_ttime[a_idx];
+	bfqq->io_start_time = bic->saved_io_start_time[a_idx];
+	bfqq->tot_idle_time = bic->saved_tot_idle_time[a_idx];
 	/*
 	 * Restore weight coefficient only if low_latency is on
 	 */
 	if (bfqd->low_latency) {
 		old_wr_coeff = bfqq->wr_coeff;
-		bfqq->wr_coeff = bic->saved_wr_coeff;
+		bfqq->wr_coeff = bic->saved_wr_coeff[a_idx];
 	}
-	bfqq->service_from_wr = bic->saved_service_from_wr;
-	bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
-	bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
-	bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
+	bfqq->service_from_wr = bic->saved_service_from_wr[a_idx];
+	bfqq->wr_start_at_switch_to_srt =
+				bic->saved_wr_start_at_switch_to_srt[a_idx];
+	bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish[a_idx];
+	bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time[a_idx];
 
 	if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
 	    time_is_before_jiffies(bfqq->last_wr_start_finish +
@@ -1824,6 +1826,16 @@ 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,
@@ -1878,7 +1890,9 @@ 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)->stably_merged) &&
+		  (bfqq->bic ||
+		   RQ_BIC(rq)->stably_merged
+		   [bfq_actuator_index(bfqd, rq->bio)]) &&
 		   (*interactive || soft_rt)));
 
 	/*
@@ -2466,16 +2480,6 @@ 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)
 {
@@ -2902,6 +2906,7 @@ 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;
+	unsigned int a_idx = bfqq->actuator_idx;
 
 	/* if a merge has already been setup, then proceed with that first */
 	if (bfqq->new_bfqq)
@@ -2923,21 +2928,21 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		 * stable merging) also if bic is associated with a
 		 * sync queue, but this bfqq is async
 		 */
-		if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq &&
+		if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq[a_idx] &&
 		    !bfq_bfqq_just_created(bfqq) &&
 		    time_is_before_jiffies(bfqq->split_time +
 					  msecs_to_jiffies(bfq_late_stable_merging)) &&
 		    time_is_before_jiffies(bfqq->creation_time +
 					   msecs_to_jiffies(bfq_late_stable_merging))) {
 			struct bfq_queue *stable_merge_bfqq =
-				bic->stable_merge_bfqq;
+				bic->stable_merge_bfqq[a_idx];
 			int proc_ref = min(bfqq_process_refs(bfqq),
 					   bfqq_process_refs(stable_merge_bfqq));
 
 			/* deschedule stable merge, because done or aborted here */
 			bfq_put_stable_ref(stable_merge_bfqq);
 
-			bic->stable_merge_bfqq = NULL;
+			bic->stable_merge_bfqq[a_idx] = NULL;
 
 			if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
 			    proc_ref > 0) {
@@ -2946,9 +2951,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 					bfq_setup_merge(bfqq, stable_merge_bfqq);
 
 				if (new_bfqq) {
-					bic->stably_merged = true;
+					bic->stably_merged[a_idx] = true;
 					if (new_bfqq->bic)
-						new_bfqq->bic->stably_merged =
+						new_bfqq->bic->stably_merged
+						    [new_bfqq->actuator_idx] =
 									true;
 				}
 				return new_bfqq;
@@ -3048,6 +3054,8 @@ 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;
+	/* State must be saved for the right queue index. */
+	unsigned int a_idx = bfqq->actuator_idx;
 
 	/*
 	 * If !bfqq->bic, the queue is already shared or its requests
@@ -3057,18 +3065,18 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
 	if (!bic)
 		return;
 
-	bic->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
-	bic->saved_inject_limit = bfqq->inject_limit;
-	bic->saved_decrease_time_jif = bfqq->decrease_time_jif;
-
-	bic->saved_weight = bfqq->entity.orig_weight;
-	bic->saved_ttime = bfqq->ttime;
-	bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
-	bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
-	bic->saved_io_start_time = bfqq->io_start_time;
-	bic->saved_tot_idle_time = bfqq->tot_idle_time;
-	bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
-	bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
+	bic->saved_last_serv_time_ns[a_idx] = bfqq->last_serv_time_ns;
+	bic->saved_inject_limit[a_idx] = bfqq->inject_limit;
+	bic->saved_decrease_time_jif[a_idx] = bfqq->decrease_time_jif;
+
+	bic->saved_weight[a_idx] = bfqq->entity.orig_weight;
+	bic->saved_ttime[a_idx] = bfqq->ttime;
+	bic->saved_has_short_ttime[a_idx] = bfq_bfqq_has_short_ttime(bfqq);
+	bic->saved_IO_bound[a_idx] = bfq_bfqq_IO_bound(bfqq);
+	bic->saved_io_start_time[a_idx] = bfqq->io_start_time;
+	bic->saved_tot_idle_time[a_idx] = bfqq->tot_idle_time;
+	bic->saved_in_large_burst[a_idx] = bfq_bfqq_in_large_burst(bfqq);
+	bic->was_in_burst_list[a_idx] = !hlist_unhashed(&bfqq->burst_list_node);
 	if (unlikely(bfq_bfqq_just_created(bfqq) &&
 		     !bfq_bfqq_in_large_burst(bfqq) &&
 		     bfqq->bfqd->low_latency)) {
@@ -3081,17 +3089,17 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
 		 * to bfqq, so that to avoid that bfqq unjustly fails
 		 * to enjoy weight raising if split soon.
 		 */
-		bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
-		bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
-		bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
-		bic->saved_last_wr_start_finish = jiffies;
+		bic->saved_wr_coeff[a_idx] = bfqq->bfqd->bfq_wr_coeff;
+		bic->saved_wr_start_at_switch_to_srt[a_idx] = bfq_smallest_from_now();
+		bic->saved_wr_cur_max_time[a_idx] = bfq_wr_duration(bfqq->bfqd);
+		bic->saved_last_wr_start_finish[a_idx] = jiffies;
 	} else {
-		bic->saved_wr_coeff = bfqq->wr_coeff;
-		bic->saved_wr_start_at_switch_to_srt =
+		bic->saved_wr_coeff[a_idx] = bfqq->wr_coeff;
+		bic->saved_wr_start_at_switch_to_srt[a_idx] =
 			bfqq->wr_start_at_switch_to_srt;
-		bic->saved_service_from_wr = bfqq->service_from_wr;
-		bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
-		bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
+		bic->saved_service_from_wr[a_idx] = bfqq->service_from_wr;
+		bic->saved_last_wr_start_finish[a_idx] = bfqq->last_wr_start_finish;
+		bic->saved_wr_cur_max_time[a_idx] = bfqq->wr_cur_max_time;
 	}
 }
 
@@ -5423,8 +5431,8 @@ static void bfq_exit_icq(struct io_cq *icq)
 		spin_lock_irqsave(&bfqd->lock, flags);
 
 	for (act_idx = 0; act_idx < BFQ_NUM_ACTUATORS; act_idx++) {
-		if (bic->stable_merge_bfqq)
-			bfq_put_stable_ref(bic->stable_merge_bfqq);
+		if (bic->stable_merge_bfqq[act_idx])
+			bfq_put_stable_ref(bic->stable_merge_bfqq[act_idx]);
 
 		bfq_exit_icq_bfqq(bic, true, act_idx);
 		bfq_exit_icq_bfqq(bic, false, act_idx);
@@ -5612,6 +5620,7 @@ 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);
 
@@ -5619,8 +5628,8 @@ bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		return bfqq;
 
 	if (new_bfqq->bic)
-		new_bfqq->bic->stably_merged = true;
-	bic->stably_merged = true;
+		new_bfqq->bic->stably_merged[a_idx] = true;
+	bic->stably_merged[a_idx] = true;
 
 	/*
 	 * Reusing merge functions. This implies that
@@ -5750,7 +5759,8 @@ static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
 			/*
 			 * Record the bfqq to merge to.
 			 */
-			bic->stable_merge_bfqq = last_bfqq_created;
+			bic->stable_merge_bfqq[last_bfqq_created->actuator_idx]
+							   = last_bfqq_created;
 		}
 	}
 
@@ -6684,12 +6694,12 @@ static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
 
 	bic_set_bfqq(bic, bfqq, is_sync, act_idx);
 	if (split && is_sync) {
-		if ((bic->was_in_burst_list && bfqd->large_burst) ||
-		    bic->saved_in_large_burst)
+		if ((bic->was_in_burst_list[act_idx] && bfqd->large_burst) ||
+		    bic->saved_in_large_burst[act_idx])
 			bfq_mark_bfqq_in_large_burst(bfqq);
 		else {
 			bfq_clear_bfqq_in_large_burst(bfqq);
-			if (bic->was_in_burst_list)
+			if (bic->was_in_burst_list[act_idx])
 				/*
 				 * If bfqq was in the current
 				 * burst list before being
@@ -6778,6 +6788,7 @@ 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;
+	unsigned int a_idx = bfq_actuator_index(bfqd, bio);
 
 	if (unlikely(!rq->elv.icq))
 		return NULL;
@@ -6804,12 +6815,12 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
 	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) &&
-			!bic->stably_merged) {
+			!bic->stably_merged[a_idx]) {
 			struct bfq_queue *old_bfqq = bfqq;
 
 			/* Update bic before losing reference to bfqq */
 			if (bfq_bfqq_in_large_burst(bfqq))
-				bic->saved_in_large_burst = true;
+				bic->saved_in_large_burst[a_idx] = true;
 
 			bfqq = bfq_split_bfqq(bic, bfqq);
 			split = true;
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 8b5225a9e080..0ff6be18f72a 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -431,30 +431,37 @@ struct bfq_io_cq {
 	uint64_t blkcg_serial_nr; /* the current blkcg serial */
 #endif
 	/*
-	 * Snapshot of the has_short_time flag before merging; taken
-	 * to remember its value while the queue is merged, so as to
-	 * be able to restore it in case of split.
+	 * Several fields follow, which are used to support
+	 * queue-merging operations. Each field is an array, because a
+	 * process may be associated with multiple bfq_queues (see the
+	 * field bfqq above). And each of these queues may undergo a
+	 * merge.
 	 */
-	bool saved_has_short_ttime;
+	/*
+	 * Snapshot of the has_short_time flags before merging; taken
+	 * to remember their values while a queue is merged, so as to
+	 * be able to restore them in case of split.
+	 */
+	bool saved_has_short_ttime[BFQ_NUM_ACTUATORS];
 	/*
 	 * Same purpose as the previous two fields for the I/O bound
 	 * classification of a queue.
 	 */
-	bool saved_IO_bound;
+	bool saved_IO_bound[BFQ_NUM_ACTUATORS];
 
-	u64 saved_io_start_time;
-	u64 saved_tot_idle_time;
+	u64 saved_io_start_time[BFQ_NUM_ACTUATORS];
+	u64 saved_tot_idle_time[BFQ_NUM_ACTUATORS];
 
 	/*
-	 * 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;
+	bool saved_in_large_burst[BFQ_NUM_ACTUATORS];
 	/*
 	 * True if the queue belonged to a burst list before its merge
 	 * with another cooperating queue.
 	 */
-	bool was_in_burst_list;
+	bool was_in_burst_list[BFQ_NUM_ACTUATORS];
 
 	/*
 	 * Save the weight when a merge occurs, to be able
@@ -463,27 +470,28 @@ struct bfq_io_cq {
 	 * then the weight of the recycled queue could differ
 	 * from the weight of the original queue.
 	 */
-	unsigned int saved_weight;
+	unsigned int saved_weight[BFQ_NUM_ACTUATORS];
 
 	/*
 	 * Similar to previous fields: save wr information.
 	 */
-	unsigned long saved_wr_coeff;
-	unsigned long saved_last_wr_start_finish;
-	unsigned long saved_service_from_wr;
-	unsigned long saved_wr_start_at_switch_to_srt;
-	unsigned int saved_wr_cur_max_time;
-	struct bfq_ttime saved_ttime;
+	unsigned long saved_wr_coeff[BFQ_NUM_ACTUATORS];
+	unsigned long saved_last_wr_start_finish[BFQ_NUM_ACTUATORS];
+	unsigned long saved_service_from_wr[BFQ_NUM_ACTUATORS];
+	unsigned long saved_wr_start_at_switch_to_srt[BFQ_NUM_ACTUATORS];
+	unsigned int saved_wr_cur_max_time[BFQ_NUM_ACTUATORS];
+	struct bfq_ttime saved_ttime[BFQ_NUM_ACTUATORS];
 
 	/* Save also injection state */
-	u64 saved_last_serv_time_ns;
-	unsigned int saved_inject_limit;
-	unsigned long saved_decrease_time_jif;
+	u64 saved_last_serv_time_ns[BFQ_NUM_ACTUATORS];
+	unsigned int saved_inject_limit[BFQ_NUM_ACTUATORS];
+	unsigned long saved_decrease_time_jif[BFQ_NUM_ACTUATORS];
 
 	/* candidate queue for a stable merge (due to close creation time) */
-	struct bfq_queue *stable_merge_bfqq;
+	struct bfq_queue *stable_merge_bfqq[BFQ_NUM_ACTUATORS];
+
+	bool stably_merged[BFQ_NUM_ACTUATORS];	/* non splittable if true */
 
-	bool stably_merged;	/* non splittable if true */
 	unsigned int requests;	/* Number of requests this process has in flight */
 };
 
-- 
2.20.1