[PATCH v2 1/2] block: Introduce nr_sched_batch sys interface

[Wang You <wangyoua@xxxxxxxxxxxxx>]

The function of this patch is to add an nr_sched_batch interface under
/sys/block/sdx/queue/, which can be used to set the number of batching
requests. Of course, the default value is nr_requests and will follow
nr_request when it has not been changed.

Signed-off-by: Wang You <wangyoua@xxxxxxxxxxxxx>
---
 block/blk-mq-sched.c   |  4 +++-
 block/blk-sysfs.c      | 32 ++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |  1 +
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index a4f7c101b53b..92798a0c03bd 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -100,7 +100,7 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 	if (hctx->dispatch_busy)
 		max_dispatch = 1;
 	else
-		max_dispatch = hctx->queue->nr_requests;
+		max_dispatch = q->nr_sched_batch;
 
 	do {
 		struct request *rq;
@@ -567,6 +567,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 		blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
 		q->elevator = NULL;
 		q->nr_requests = q->tag_set->queue_depth;
+		q->nr_sched_batch = q->nr_requests;
 		return 0;
 	}
 
@@ -577,6 +578,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 	 */
 	q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 				   BLKDEV_DEFAULT_RQ);
+	q->nr_sched_batch = q->nr_requests;
 
 	if (blk_mq_is_shared_tags(flags)) {
 		ret = blk_mq_init_sched_shared_tags(q);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 9b905e9443e4..34fbfb22e3e1 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -70,6 +70,7 @@ queue_requests_store(struct request_queue *q, const char *page, size_t count)
 {
 	unsigned long nr;
 	int ret, err;
+	unsigned long prev_nr_request = q->nr_requests;
 
 	if (!queue_is_mq(q))
 		return -EINVAL;
@@ -85,6 +86,35 @@ queue_requests_store(struct request_queue *q, const char *page, size_t count)
 	if (err)
 		return err;
 
+	if (q->nr_sched_batch == prev_nr_request || q->nr_sched_batch > nr)
+		q->nr_sched_batch = nr;
+
+	return ret;
+}
+
+static ssize_t elv_nr_batch_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(q->nr_sched_batch, page);
+}
+
+static ssize_t elv_nr_batch_store(struct request_queue *q, const char *page,
+				  size_t count)
+{
+	unsigned long nr;
+	int ret;
+
+	if (!queue_is_mq(q))
+		return -EINVAL;
+
+	ret = queue_var_store(&nr, page, count);
+	if (ret < 0)
+		return ret;
+
+	if (nr > q->nr_requests || nr < 1)
+		return -EINVAL;
+
+	q->nr_sched_batch = nr;
+
 	return ret;
 }
 
@@ -573,6 +603,7 @@ QUEUE_RO_ENTRY(queue_max_segments, "max_segments");
 QUEUE_RO_ENTRY(queue_max_integrity_segments, "max_integrity_segments");
 QUEUE_RO_ENTRY(queue_max_segment_size, "max_segment_size");
 QUEUE_RW_ENTRY(elv_iosched, "scheduler");
+QUEUE_RW_ENTRY(elv_nr_batch, "nr_sched_batch");
 
 QUEUE_RO_ENTRY(queue_logical_block_size, "logical_block_size");
 QUEUE_RO_ENTRY(queue_physical_block_size, "physical_block_size");
@@ -632,6 +663,7 @@ static struct attribute *queue_attrs[] = {
 	&queue_max_integrity_segments_entry.attr,
 	&queue_max_segment_size_entry.attr,
 	&elv_iosched_entry.attr,
+	&elv_nr_batch_entry.attr,
 	&queue_hw_sector_size_entry.attr,
 	&queue_logical_block_size_entry.attr,
 	&queue_physical_block_size_entry.attr,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2f7b43444c5f..e38eba4161a3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -422,6 +422,7 @@ struct request_queue {
 	 * queue settings
 	 */
 	unsigned long		nr_requests;	/* Max # of requests */
+	unsigned long nr_sched_batch;
 
 	unsigned int		dma_pad_mask;
 	unsigned int		dma_alignment;
-- 
2.27.0