On 30/04/2020 14:18, Hannes Reinecke wrote:
From: Hannes Reinecke <hare@xxxxxxxx>
Quite a lot of 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@xxxxxxxx>
It may be worth adding this field to scsi_host_template. And we should
also prob mention this in Documentation/scsi/scsi_mid_low_api.txt
Apart from that, thanks:
Reviewed-by: John Garry <john.garry@xxxxxxxxxx>
---
drivers/scsi/scsi_lib.c | 1 +
include/scsi/scsi_host.h | 6 ++++++
2 files changed, 7 insertions(+)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 47835c4b4ee0..5358f553f526 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1885,6 +1885,7 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
shost->tag_set.ops = &scsi_mq_ops_no_commit;
shost->tag_set.nr_hw_queues = shost->nr_hw_queues ? : 1;
shost->tag_set.queue_depth = shost->can_queue;
+ shost->tag_set.reserved_tags = shost->nr_reserved_cmds;
shost->tag_set.cmd_size = cmd_size;
shost->tag_set.numa_node = NUMA_NO_NODE;
shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 822e8cda8d9b..37bb7d74e4c4 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -599,6 +599,12 @@ struct Scsi_Host {
* is nr_hw_queues * can_queue.
*/
unsigned nr_hw_queues;
+
+ /*
+ * Number of commands to reserve, if any.
+ */
+ unsigned nr_reserved_cmds;
+
unsigned active_mode:2;
unsigned unchecked_isa_dma:1;
