[PATCH v2 06/20] scsi: core: Add support for reserved tags

Bart Van Assche
2021-11-19T19:58:07Z

Allow SCSI LLDs to allocate reserved tags by passing the BLK_MQ_REQ_RESERVED
flag to blk_mq_alloc_request().

Cc: Hannes Reinecke <hare@suse.de>
Cc: John Garry <john.garry@huawei.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
drivers/scsi/scsi_lib.c | 4 +++-
include/scsi/scsi_host.h | 9 ++++++++-
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 59c3c4fbcfc0..44489ddc646c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1925,6 +1925,7 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
{
unsigned int cmd_size, sgl_size;
struct blk_mq_tag_set *tag_set = &shost->tag_set;
+ unsigned int reserved_tags = shost->hostt->reserved_tags;

sgl_size = max_t(unsigned int, sizeof(struct scatterlist),
scsi_mq_inline_sgl_size(shost));
@@ -1940,7 +1941,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
tag_set->ops = &scsi_mq_ops_no_commit;
tag_set->nr_hw_queues = shost->nr_hw_queues ? : 1;
tag_set->nr_maps = shost->nr_maps ? : 1;
- tag_set->queue_depth = shost->can_queue;
+ tag_set->queue_depth = shost->can_queue + reserved_tags;
+ tag_set->reserved_tags = reserved_tags;
tag_set->cmd_size = cmd_size;
tag_set->numa_node = NUMA_NO_NODE;
tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 72e1a347baa6..ec0f7705e06a 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -367,10 +367,17 @@ struct scsi_host_template {
/*
* This determines if we will use a non-interrupt driven
* or an interrupt driven scheme. It is set to the maximum number
- * of simultaneous commands a single hw queue in HBA will accept.
+ * of simultaneous commands a single hw queue in HBA will accept. Does
+ * not include @reserved_tags.
*/
int can_queue;

+ /*
+ * Number of tags to reserve. A reserved tag can be allocated by passing
+ * the BLK_MQ_REQ_RESERVED flag to blk_get_request().
+ */
+ unsigned reserved_tags;
+
/*
* In many instances, especially where disconnect / reconnect are
* supported, our host also has an ID on the SCSI bus. If this is