On 6/25/20 5:30 PM, John Garry wrote:
On 25/06/2020 15:01, Hannes Reinecke wrote:
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@xxxxxxx>
---
drivers/scsi/scsi_lib.c | 10 +++++++++-
include/scsi/scsi_host.h | 11 +++++++++++
2 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index bd378e1bd3fc..a752806af70b 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1887,7 +1887,9 @@ 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->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 = NUMA_NO_NODE;
tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
@@ -1910,6 +1912,9 @@ void scsi_mq_destroy_tags(struct Scsi_Host *shost)
* @op_flags: request allocation flags
*
* Allocates a SCSI command for internal LLDD use.
+ * If 'nr_reserved_commands' is spectified by the host the
/s/spectified/specified/
I suppose making this usable by drivers which don't set
nr_reserved_commands is helpful (if not slightly strange). In that we
can move drivers which don't use rq->tag currently - like pm8001 - to
use it, and not have to worry about guessing some nr_reserved_commands
to specify.
That's what I plan to do, and in fact have patches queued for that.
I've just posted the initial patchset here to agree on the interface
and provide drivers which benefit from it with very little churn.
In a later patchset I'll be converting other drivers and subsystems like
megaraid_sas and libsas etc; those I had in the v3 version but that was
deemed to complex for the initial submission.
Hence I've left them out in this round.
+ * command will be allocated from the reserved tag pool;
+ * otherwise the normal tag pool will be used.
*/
struct scsi_cmnd *scsi_get_internal_cmd(struct scsi_device *sdev,
int data_direction, int op_flags)
@@ -1919,6 +1924,9 @@ struct scsi_cmnd *scsi_get_internal_cmd(struct
scsi_device *sdev,
blk_mq_req_flags_t flags = 0;
unsigned int op = REQ_INTERNAL | op_flags;
+ if (sdev->host->nr_reserved_cmds)
+ flags = BLK_MQ_REQ_RESERVED; > +
op |= (data_direction == DMA_TO_DEVICE) ?
REQ_OP_SCSI_OUT : REQ_OP_SCSI_IN;
rq = blk_mq_alloc_request(sdev->request_queue, op, flags);
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 46ef8cccc982..b94938e87e3a 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -590,6 +590,11 @@ 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;
@@ -606,6 +611,12 @@ struct Scsi_Host {
* is nr_hw_queues * can_queue.
If we are going to go this way, then could you update the comment on
Scsi_Host.nr_hw_queues here? Currently we have "it is assumed that each
hardware queue has a depth of can_queue..."
Ah. Right. Yes, will do.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
