linux-kernel - [PATCH V7 6/8] block, bfq: retrieve independent access ranges from request queue

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Date:   Tue,  6 Dec 2022 09:15:49 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        arie.vanderhoeven@...gate.com, rory.c.chen@...gate.com,
        glen.valante@...aro.org, Federico Gavioli <f.gavioli97@...il.com>,
        Paolo Valente <paolo.valente@...aro.org>
Subject: [PATCH V7 6/8] block, bfq: retrieve independent access ranges from request queue

From: Federico Gavioli <f.gavioli97@...il.com>

This patch implements the code to gather the content of the
independent_access_ranges structure from the request_queue and copy
it into the queue's bfq_data. This copy is done at queue initialization.

We copy the access ranges into the bfq_data to avoid taking the queue
lock each time we access the ranges.

This implementation, however, puts a limit to the maximum independent
ranges supported by the scheduler. Such a limit is equal to the constant
BFQ_MAX_ACTUATORS. This limit was placed to avoid the allocation of
dynamic memory.

Co-developed-by: Rory Chen <rory.c.chen@...gate.com>
Signed-off-by: Rory Chen <rory.c.chen@...gate.com>
Signed-off-by: Federico Gavioli <f.gavioli97@...il.com>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-iosched.c | 56 ++++++++++++++++++++++++++++++++++++++-------
 block/bfq-iosched.h |  8 ++++++-
 2 files changed, 55 insertions(+), 9 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 6b1376ab8980..665e78035666 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1838,10 +1838,25 @@ static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
  */
 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 (to keep incomplete mechanisms off).
-	 */
+	unsigned int i;
+	sector_t end;
+
+	/* no search needed if one or zero ranges present */
+	if (bfqd->num_actuators < 2)
+		return 0;
+
+	/* bio_end_sector(bio) gives the sector after the last one */
+	end = bio_end_sector(bio) - 1;
+
+	for (i = 0; i < bfqd->num_actuators; i++) {
+		if (end >= bfqd->sector[i] &&
+		    end < bfqd->sector[i] + bfqd->nr_sectors[i])
+			return i;
+	}
+
+	WARN_ONCE(true,
+		  "bfq_actuator_index: bio sector out of ranges: end=%llu\n",
+		  end);
 	return 0;
 }
 
@@ -7159,6 +7174,8 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 {
 	struct bfq_data *bfqd;
 	struct elevator_queue *eq;
+	unsigned int i;
+	struct blk_independent_access_ranges *ia_ranges = q->disk->ia_ranges;
 
 	eq = elevator_alloc(q, e);
 	if (!eq)
@@ -7202,11 +7219,34 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	bfqd->queue = q;
 
 	/*
-	 * Multi-actuator support not complete yet, unconditionally
-	 * set to only one actuator for the moment (to keep incomplete
-	 * mechanisms off).
+	 * If the disk supports multiple actuators, copy independent
+	 * access ranges from the request queue structure.
 	 */
-	bfqd->num_actuators = 1;
+	spin_lock_irq(&q->queue_lock);
+	if (ia_ranges) {
+		/*
+		 * Check if the disk ia_ranges size exceeds the current bfq
+		 * actuator limit.
+		 */
+		if (ia_ranges->nr_ia_ranges > BFQ_MAX_ACTUATORS) {
+			pr_crit("nr_ia_ranges higher than act limit: iars=%d, max=%d.\n",
+				ia_ranges->nr_ia_ranges, BFQ_MAX_ACTUATORS);
+			pr_crit("Falling back to single actuator mode.\n");
+			bfqd->num_actuators = 0;
+		} else {
+			bfqd->num_actuators = ia_ranges->nr_ia_ranges;
+
+			for (i = 0; i < bfqd->num_actuators; i++) {
+				bfqd->sector[i] = ia_ranges->ia_range[i].sector;
+				bfqd->nr_sectors[i] =
+					ia_ranges->ia_range[i].nr_sectors;
+			}
+		}
+	} else {
+		bfqd->num_actuators = 0;
+	}
+
+	spin_unlock_irq(&q->queue_lock);
 
 	INIT_LIST_HEAD(&bfqd->dispatch);
 
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 1450990dba32..953980de6b4b 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -810,7 +810,13 @@ struct bfq_data {
 	 * case of single-actuator drives.
 	 */
 	unsigned int num_actuators;
-
+	/*
+	 * Disk independent access ranges for each actuator
+	 * in this device.
+	 */
+	sector_t sector[BFQ_MAX_ACTUATORS];
+	sector_t nr_sectors[BFQ_MAX_ACTUATORS];
+	struct blk_independent_access_range ia_ranges[BFQ_MAX_ACTUATORS];
 };
 
 enum bfqq_state_flags {
-- 
2.20.1