summaryrefslogtreecommitdiff
path: root/Documentation/block
diff options
context:
space:
mode:
authorJens Axboe <axboe@kernel.dk>2018-10-24 12:39:36 +0300
committerJens Axboe <axboe@kernel.dk>2018-11-07 23:42:32 +0300
commit7ca01926463a15f5d2681458643b2453930b873a (patch)
tree06ea203ffd839dfb7dfe0be9a10287679b898d36 /Documentation/block
parent2cdf2caecda6cb16c24c6bdd2484d4cec99cfbb3 (diff)
downloadlinux-7ca01926463a15f5d2681458643b2453930b873a.tar.xz
block: remove legacy rq tagging
It's now unused, kill it. Reviewed-by: Hannes Reinecke <hare@suse.com> Tested-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'Documentation/block')
-rw-r--r--Documentation/block/biodoc.txt88
1 files changed, 0 insertions, 88 deletions
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index 207eca58efaa..ac18b488cb5e 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -65,7 +65,6 @@ Description of Contents:
3.2.3 I/O completion
3.2.4 Implications for drivers that do not interpret bios (don't handle
multiple segments)
- 3.2.5 Request command tagging
3.3 I/O submission
4. The I/O scheduler
5. Scalability related changes
@@ -708,93 +707,6 @@ is crossed on completion of a transfer. (The end*request* functions should
be used if only if the request has come down from block/bio path, not for
direct access requests which only specify rq->buffer without a valid rq->bio)
-3.2.5 Generic request command tagging
-
-3.2.5.1 Tag helpers
-
-Block now offers some simple generic functionality to help support command
-queueing (typically known as tagged command queueing), ie manage more than
-one outstanding command on a queue at any given time.
-
- blk_queue_init_tags(struct request_queue *q, int depth)
-
- Initialize internal command tagging structures for a maximum
- depth of 'depth'.
-
- blk_queue_free_tags((struct request_queue *q)
-
- Teardown tag info associated with the queue. This will be done
- automatically by block if blk_queue_cleanup() is called on a queue
- that is using tagging.
-
-The above are initialization and exit management, the main helpers during
-normal operations are:
-
- blk_queue_start_tag(struct request_queue *q, struct request *rq)
-
- Start tagged operation for this request. A free tag number between
- 0 and 'depth' is assigned to the request (rq->tag holds this number),
- and 'rq' is added to the internal tag management. If the maximum depth
- for this queue is already achieved (or if the tag wasn't started for
- some other reason), 1 is returned. Otherwise 0 is returned.
-
- blk_queue_end_tag(struct request_queue *q, struct request *rq)
-
- End tagged operation on this request. 'rq' is removed from the internal
- book keeping structures.
-
-To minimize struct request and queue overhead, the tag helpers utilize some
-of the same request members that are used for normal request queue management.
-This means that a request cannot both be an active tag and be on the queue
-list at the same time. blk_queue_start_tag() will remove the request, but
-the driver must remember to call blk_queue_end_tag() before signalling
-completion of the request to the block layer. This means ending tag
-operations before calling end_that_request_last()! For an example of a user
-of these helpers, see the IDE tagged command queueing support.
-
-3.2.5.2 Tag info
-
-Some block functions exist to query current tag status or to go from a
-tag number to the associated request. These are, in no particular order:
-
- blk_queue_tagged(q)
-
- Returns 1 if the queue 'q' is using tagging, 0 if not.
-
- blk_queue_tag_request(q, tag)
-
- Returns a pointer to the request associated with tag 'tag'.
-
- blk_queue_tag_depth(q)
-
- Return current queue depth.
-
- blk_queue_tag_queue(q)
-
- Returns 1 if the queue can accept a new queued command, 0 if we are
- at the maximum depth already.
-
- blk_queue_rq_tagged(rq)
-
- Returns 1 if the request 'rq' is tagged.
-
-3.2.5.2 Internal structure
-
-Internally, block manages tags in the blk_queue_tag structure:
-
- struct blk_queue_tag {
- struct request **tag_index; /* array or pointers to rq */
- unsigned long *tag_map; /* bitmap of free tags */
- struct list_head busy_list; /* fifo list of busy tags */
- int busy; /* queue depth */
- int max_depth; /* max queue depth */
- };
-
-Most of the above is simple and straight forward, however busy_list may need
-a bit of explaining. Normally we don't care too much about request ordering,
-but in the event of any barrier requests in the tag queue we need to ensure
-that requests are restarted in the order they were queue.
-
3.3 I/O Submission
The routine submit_bio() is used to submit a single io. Higher level i/o