[PATCH v16 20/26] blk-zoned: Support pipelining of zoned writes

[Bart Van Assche <bvanassche@acm.org>]

Support pipelining of zoned writes if the block driver preserves the write
order per hardware queue. Track per zone to which software queue writes
have been queued. If zoned writes are pipelined, submit new writes to the
same software queue as the writes that are already in progress. This
prevents reordering by submitting requests for the same zone to different
software or hardware queues.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-zoned.c | 40 ++++++++++++++++++++++++++++------------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 8d0fac14c837..f934c0cb5fdd 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -8,6 +8,7 @@
  * Copyright (c) 2016, Damien Le Moal
  * Copyright (c) 2016, Western Digital
  * Copyright (c) 2024, Western Digital Corporation or its affiliates.
+ * Copyright 2024 Google LLC
  */
 
 #include <linux/kernel.h>
@@ -59,6 +60,8 @@ static const char *const zone_cond_name[] = {
  *             as a number of 512B sectors.
  * @wp_offset_compl: End offset for completed zoned writes as a number of 512
  *		     byte sectors.
+ * @swq_cpu: Software queue to submit writes to for drivers that preserve the
+ *	write order.
  * @bio_list: The list of BIOs that are currently plugged.
  * @bio_work: Work struct to handle issuing of plugged BIOs
  * @rcu_head: RCU head to free zone write plugs with an RCU grace period.
@@ -73,6 +76,7 @@ struct blk_zone_wplug {
 	unsigned int		zone_no;
 	unsigned int		wp_offset;
 	unsigned int		wp_offset_compl;
+	int			swq_cpu;
 	struct bio_list		bio_list;
 	struct work_struct	bio_work;
 	struct rcu_head		rcu_head;
@@ -82,8 +86,7 @@ struct blk_zone_wplug {
 /*
  * Zone write plug flags bits:
  *  - BLK_ZONE_WPLUG_PLUGGED: Indicates that the zone write plug is plugged,
- *    that is, that write BIOs are being throttled due to a write BIO already
- *    being executed or the zone write plug bio list is not empty.
+ *    that is, that write BIOs are being throttled.
  *  - BLK_ZONE_WPLUG_ERROR: Indicates that a write error happened which will be
  *    recovered with a report zone to update the zone write pointer offset.
  *  - BLK_ZONE_WPLUG_UNHASHED: Indicates that the zone write plug was removed
@@ -535,6 +538,7 @@ static struct blk_zone_wplug *disk_get_and_lock_zone_wplug(struct gendisk *disk,
 	zwplug->zone_no = zno;
 	zwplug->wp_offset = sector & (disk->queue->limits.chunk_sectors - 1);
 	zwplug->wp_offset_compl = 0;
+	zwplug->swq_cpu = -1;
 	bio_list_init(&zwplug->bio_list);
 	INIT_WORK(&zwplug->bio_work, blk_zone_wplug_bio_work);
 	zwplug->disk = disk;
@@ -973,7 +977,8 @@ static bool blk_zone_wplug_prepare_bio(struct blk_zone_wplug *zwplug,
 	return false;
 }
 
-static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
+static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs,
+					int *swq_cpu)
 {
 	struct gendisk *disk = bio->bi_bdev->bd_disk;
 	sector_t sector = bio->bi_iter.bi_sector;
@@ -1017,11 +1022,19 @@ static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
 	bio_set_flag(bio, BIO_ZONE_WRITE_PLUGGING);
 
 	/*
-	 * If the zone is already plugged or has a pending error, add the BIO
-	 * to the plug BIO list. Otherwise, plug and let the BIO execute.
+	 * If the zone has a pending error or is already plugged, add the BIO
+	 * to the plug BIO list. Otherwise, execute the BIO and plug if not yet
+	 * plugged and if the write order is not preserved.
 	 */
-	if (zwplug->flags & BLK_ZONE_WPLUG_BUSY)
+	if (zwplug->flags & BLK_ZONE_WPLUG_BUSY) {
 		goto plug;
+	} else if (disk->queue->limits.driver_preserves_write_order) {
+		if (zwplug->swq_cpu < 0)
+			zwplug->swq_cpu = raw_smp_processor_id();
+		*swq_cpu = zwplug->swq_cpu;
+	} else {
+		zwplug->flags |= BLK_ZONE_WPLUG_PLUGGED;
+	}
 
 	/*
 	 * If an error is detected when preparing the BIO, add it to the BIO
@@ -1030,8 +1043,6 @@ static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
 	if (!blk_zone_wplug_prepare_bio(zwplug, bio))
 		goto plug;
 
-	zwplug->flags |= BLK_ZONE_WPLUG_PLUGGED;
-
 	spin_unlock_irqrestore(&zwplug->lock, flags);
 
 	return false;
@@ -1107,7 +1118,7 @@ bool blk_zone_plug_bio(struct bio *bio, unsigned int nr_segs, int *swq_cpu)
 		fallthrough;
 	case REQ_OP_WRITE:
 	case REQ_OP_WRITE_ZEROES:
-		return blk_zone_wplug_handle_write(bio, nr_segs);
+		return blk_zone_wplug_handle_write(bio, nr_segs, swq_cpu);
 	case REQ_OP_ZONE_RESET:
 		return blk_zone_wplug_handle_reset_or_finish(bio, 0);
 	case REQ_OP_ZONE_FINISH:
@@ -1131,7 +1142,6 @@ static void disk_zone_wplug_schedule_bio_work(struct gendisk *disk,
 	 * of the next plugged BIO. blk_zone_wplug_bio_work() will release the
 	 * reference we take here.
 	 */
-	WARN_ON_ONCE(!(zwplug->flags & BLK_ZONE_WPLUG_PLUGGED));
 	refcount_inc(&zwplug->ref);
 	queue_work(disk->zone_wplugs_wq, &zwplug->bio_work);
 }
@@ -1185,6 +1195,9 @@ static void disk_zone_wplug_unplug_bio(struct gendisk *disk,
 
 	zwplug->flags &= ~BLK_ZONE_WPLUG_PLUGGED;
 
+	if (refcount_read(&zwplug->ref) == 2)
+		zwplug->swq_cpu = -1;
+
 	/*
 	 * If the zone is full (it was fully written or finished, or empty
 	 * (it was reset), remove its zone write plug from the hash table.
@@ -1937,6 +1950,7 @@ static void queue_zone_wplug_show(struct blk_zone_wplug *zwplug,
 	unsigned int zwp_zone_no, zwp_ref;
 	unsigned int zwp_bio_list_size;
 	unsigned long flags;
+	int swq_cpu;
 
 	spin_lock_irqsave(&zwplug->lock, flags);
 	zwp_zone_no = zwplug->zone_no;
@@ -1945,13 +1959,15 @@ static void queue_zone_wplug_show(struct blk_zone_wplug *zwplug,
 	zwp_wp_offset = zwplug->wp_offset;
 	zwp_wp_offset_compl = zwplug->wp_offset_compl;
 	zwp_bio_list_size = bio_list_size(&zwplug->bio_list);
+	swq_cpu = zwplug->swq_cpu;
 	spin_unlock_irqrestore(&zwplug->lock, flags);
 
 	bool all_zwr_inserted = blk_zone_all_zwr_inserted(zwplug);
 
-	seq_printf(m, "zone_no %u flags 0x%x ref %u wp_offset %u wp_offset_compl %u bio_list_size %u all_zwr_inserted %d\n",
+	seq_printf(m, "zone_no %u flags 0x%x ref %u wp_offset %u wp_offset_compl %u bio_list_size %u all_zwr_inserted %d swq_cpu %d\n",
 		   zwp_zone_no, zwp_flags, zwp_ref, zwp_wp_offset,
-		   zwp_wp_offset_compl, zwp_bio_list_size, all_zwr_inserted);
+		   zwp_wp_offset_compl, zwp_bio_list_size, all_zwr_inserted,
+		   swq_cpu);
 }
 
 int queue_zone_wplugs_show(void *data, struct seq_file *m)