On 5/30/19 5:48 PM, Ming Lei wrote:
On Thu, May 30, 2019 at 10:57 PM Hannes Reinecke <hare@xxxxxxx> wrote:
On 5/30/19 8:41 AM, Ming Lei wrote:
On Wed, May 29, 2019 at 03:28:39PM +0200, Hannes Reinecke wrote:
Add helper functions to retrieve SCSI commands from the reserved
tag pool.
Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
---
include/scsi/scsi_tcq.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/include/scsi/scsi_tcq.h b/include/scsi/scsi_tcq.h
index 6053d46e794e..227f3bd4e974 100644
--- a/include/scsi/scsi_tcq.h
+++ b/include/scsi/scsi_tcq.h
@@ -39,5 +39,27 @@ static inline struct scsi_cmnd *scsi_host_find_tag(struct Scsi_Host *shost,
return blk_mq_rq_to_pdu(req);
}
+static inline struct scsi_cmnd *scsi_get_reserved_cmd(struct scsi_device *sdev)
+{
+ struct request *rq;
+ struct scsi_cmnd *scmd;
+
+ rq = blk_mq_alloc_request(sdev->request_queue,
+ REQ_OP_SCSI_OUT | REQ_NOWAIT,
+ BLK_MQ_REQ_RESERVED);
+ if (IS_ERR(rq))
+ return NULL;
+ scmd = blk_mq_rq_to_pdu(rq);
+ scmd->request = rq;
+ return scmd;
+}
Now all these internal commands won't share tags with IO requests,
however, your patch switches to reserve slots for internal
commands.
Yes.
This way may have performance effect on IO workloads given the
reserved tags can't be used by IO at all.
Not really. Basically all drivers which have to use tags to send
internal commands already set some tags aside to handle internal
commands. So all this patchset does is to formalize this behaviour by
using private tags.
Some drivers (like fnic or snic) does _not_ do this currently; for those
I've set one command aside to handle command abort etc.
From hardware view, you might be right, however, the implementation
isn't correct:
set->queue_depth means number of the total tags, set->reserved_tags is just
part of the total tags, see blk_mq_init_bitmap_tags().
So any driver sets .reserved_tags > 0, tags available for IO is reduced by
same amount, isn't it? Cause .can_queue isn't increased.
Hmm. I was under the impression that the number of total tags is
set->queue_depth + set-?reserved_tags.
But reading through blk-mq-tag.c it seems you are right.
Okay, will be updating the patchset.
Cheers,
Hannes
