modified to accomplish a direct page -> bus translation, without requiring
a virtual address mapping (unlike the earlier scheme of virtual address
-> bus translation). So this works uniformly for high-memory pages (which
-do not have a correponding kernel virtual address space mapping) and
+do not have a corresponding kernel virtual address space mapping) and
low-memory pages.
Note: Please refer to DMA-mapping.txt for a discussion on PCI high mem DMA
on to the generic block layer, only to be merged by the i/o scheduler
when the underlying device was capable of handling the i/o in one shot.
Also, using the buffer head as an i/o structure for i/os that didn't originate
-from the buffer cache unecessarily added to the weight of the descriptors
+from the buffer cache unnecessarily added to the weight of the descriptors
which were generated for each such chunk.
The following were some of the goals and expectations considered in the
for raw i/o.
ii. Ability to represent high-memory buffers (which do not have a virtual
address mapping in kernel address space).
-iii.Ability to represent large i/os w/o unecessarily breaking them up (i.e
+iii.Ability to represent large i/os w/o unnecessarily breaking them up (i.e
greater than PAGE_SIZE chunks in one shot)
iv. At the same time, ability to retain independent identity of i/os from
different sources or i/o units requiring individual completion (e.g. for
latency reasons)
v. Ability to represent an i/o involving multiple physical memory segments
(including non-page aligned page fragments, as specified via readv/writev)
- without unecessarily breaking it up, if the underlying device is capable of
+ without unnecessarily breaking it up, if the underlying device is capable of
handling it.
vi. Preferably should be based on a memory descriptor structure that can be
passed around different types of subsystems or layers, maybe even
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(request_queue_t *q, int depth)
+ 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((request_queue_t *q)
+ 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
The above are initialization and exit management, the main helpers during
normal operations are:
- blk_queue_start_tag(request_queue_t *q, struct request *rq)
+ 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),
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(request_queue_t *q, struct request *rq)
+ 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.
the hardware and software block queue and enable the driver to sanely restart
all the outstanding requests. There's a third helper to do that:
- blk_queue_invalidate_tags(request_queue_t *q)
+ blk_queue_invalidate_tags(struct request_queue *q)
Clear the internal block tag queue and re-add all the pending requests
to the request queue. The driver will receive them again on the
scheduler for example, to reposition the request
if its sorting order has changed.
+elevator_allow_merge_fn called whenever the block layer determines
+ that a bio can be merged into an existing
+ request safely. The io scheduler may still
+ want to stop a merge at this point if it
+ results in some sort of conflict internally,
+ this hook allows it to do that.
+
elevator_dispatch_fn fills the dispatch queue with ready requests.
I/O schedulers are free to postpone requests by
not filling the dispatch queue unless @force
i. Binary tree
AS and deadline i/o schedulers use red black binary trees for disk position
sorting and searching, and a fifo linked list for time-based searching. This
-gives good scalability and good availablility of information. Requests are
+gives good scalability and good availability of information. Requests are
almost always dispatched in disk sort order, so a cache is kept of the next
request in sort order to prevent binary tree lookups.
projects / linux-2.6 / blobdiff