This patch aims to enable batch allocation of sufficient tags after
batch IO submission with plug mechanism, thereby avoiding the need for
frequent individual requests when the initial allocation is
insufficient.
-----------------------------------------------------------
HW:
16 CPUs/16 poll queues
Disk: Samsung PM9A3 Gen4 3.84T

CMD:
[global]
ioengine=io_uring
group_reporting=1
time_based=1
runtime=1m
refill_buffers=1
norandommap=1
randrepeat=0
fixedbufs=1
registerfiles=1
rw=randread
iodepth=128
iodepth_batch_submit=32
iodepth_batch_complete_min=32
iodepth_batch_complete_max=128
iodepth_low=32
bs=4k
numjobs=1
direct=1
hipri=1

[job1]
filename=/dev/nvme0n1
name=batch_test
------------------------------------------------------------
Perf:
base code: __blk_mq_alloc_requests() 1.47%
patch: __blk_mq_alloc_requests() 0.75%
------------------------------------------------------------

---
changes since v1:
- Modify multiple batch registrations into a single loop to achieve
  the batch quantity

changes since v2:
- Modify the call location of remainder handling
- Refactoring sbitmap cleanup time

changes since v3:
- Add handle operation in loop
- Add helper sbitmap_find_bits_in_word

changes since v4:
- Split blk-mq.c changes from sbitmap

changes since v5:
- Add workload with perf
- Modify over-counting bug

changes since v6:
- Modify parameters

Signed-off-by: hexue <xue01.he@samsung.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d626d32f6e57..6b22c2c4eb4e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -467,21 +467,26 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data)
 	unsigned long tag_mask;
 	int i, nr = 0;
 
-	tag_mask = blk_mq_get_tags(data, data->nr_tags, &tag_offset);
-	if (unlikely(!tag_mask))
-		return NULL;
+	do {
+		tag_mask = blk_mq_get_tags(data, data->nr_tags - nr, &tag_offset);
+		if (unlikely(!tag_mask)) {
+			if (nr == 0)
+				return NULL;
+			break;
+		}
+		tags = blk_mq_tags_from_data(data);
+		for (i = 0; tag_mask; i++) {
+			if (!(tag_mask & (1UL << i)))
+				continue;
+			tag = tag_offset + i;
+			prefetch(tags->static_rqs[tag]);
+			tag_mask &= ~(1UL << i);
+			rq = blk_mq_rq_ctx_init(data, tags, tag);
+			rq_list_add_head(data->cached_rqs, rq);
+			nr++;
+		}
+	} while (data->nr_tags > nr);
 
-	tags = blk_mq_tags_from_data(data);
-	for (i = 0; tag_mask; i++) {
-		if (!(tag_mask & (1UL << i)))
-			continue;
-		tag = tag_offset + i;
-		prefetch(tags->static_rqs[tag]);
-		tag_mask &= ~(1UL << i);
-		rq = blk_mq_rq_ctx_init(data, tags, tag);
-		rq_list_add_head(data->cached_rqs, rq);
-		nr++;
-	}
 	if (!(data->rq_flags & RQF_SCHED_TAGS))
 		blk_mq_add_active_requests(data->hctx, nr);
 	/* caller already holds a reference, add for remainder */
-- 
2.34.1

On Tue, 18 Nov 2025 07:32:30 +0000, Xue He wrote:
> This patch aims to enable batch allocation of sufficient tags after
> batch IO submission with plug mechanism, thereby avoiding the need for
> frequent individual requests when the initial allocation is
> insufficient.
> -----------------------------------------------------------
> HW:
> 16 CPUs/16 poll queues
> Disk: Samsung PM9A3 Gen4 3.84T
> 
> [...]

Applied, thanks!

[1/1] block: plug attempts to batch allocate tags multiple times
      commit: ddc32b7f2921c4b9f4f9a98a668b887c3514229b

Best regards,
-- 
Jens Axboe