[PATCH RFC v2 03/18] scsi: core: Implement reserved command handling

John Garry
2022-06-09T10:36:29Z

From: Hannes Reinecke <hare@suse.de>

Quite some drivers are using management commands internally, which
typically use the same hardware tag pool (ie they are being allocated
from the same hardware resources) as the 'normal' I/O commands.
These commands are set aside before allocating the block-mq tag bitmap,
so they'll never show up as busy in the tag map.
The block-layer, OTOH, already has 'reserved_tags' to handle precisely
this situation.
So this patch adds a new field 'nr_reserved_cmds' to the SCSI host
template to instruct the block layer to set aside a tag space for these
management commands by using reserved tags.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: John Garry <john.garry@huawei.com>
---
drivers/scsi/hosts.c | 3 +++
drivers/scsi/scsi_lib.c | 6 +++++-
include/scsi/scsi_host.h | 22 +++++++++++++++++++++-
3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 8352f90d997d..27296addaf63 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -474,6 +474,9 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
if (sht->virt_boundary_mask)
shost->virt_boundary_mask = sht->virt_boundary_mask;

+ if (sht->nr_reserved_cmds)
+ shost->nr_reserved_cmds = sht->nr_reserved_cmds;
+
device_initialize(&shost->shost_gendev);
dev_set_name(&shost->shost_gendev, "host%d", shost->host_no);
shost->shost_gendev.bus = &scsi_bus_type;
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 6ffc9e4258a8..f6e53c6d913c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1974,8 +1974,12 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
else
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 + shost->nr_reserved_cmds;
+ tag_set->reserved_tags = shost->nr_reserved_cmds;
+
tag_set->cmd_size = cmd_size;
tag_set->numa_node = dev_to_node(shost->dma_dev);
tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 59aef1f178f5..149dcbd4125e 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -366,10 +366,19 @@ 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
+ * excluding internal commands.
*/
int can_queue;

+ /*
+ * This determines how many commands the HBA will set aside
+ * for internal commands. This number will be added to
+ * @can_queue to calcumate the maximum number of simultaneous
+ * commands sent to the host.
+ */
+ int nr_reserved_cmds;
+
/*
* In many instances, especially where disconnect / reconnect are
* supported, our host also has an ID on the SCSI bus. If this is
@@ -602,6 +611,11 @@ struct Scsi_Host {
unsigned short max_cmd_len;

int this_id;
+
+ /*
+ * Number of commands this host can handle at the same time.
+ * This excludes reserved commands as specified by nr_reserved_cmds.
+ */
int can_queue;
short cmd_per_lun;
short unsigned int sg_tablesize;
@@ -620,6 +634,12 @@ struct Scsi_Host {
*/
unsigned nr_hw_queues;
unsigned nr_maps;
+
+ /*
+ * Number of reserved commands to allocate, if any.
+ */
+ unsigned nr_reserved_cmds;
+
unsigned active_mode:2;

/*
--
2.26.2