freebsd-dev/sys/geom/sched/subr_disk.c
Justin T. Gibbs f03f7a0ca3 Correct bioq_disksort so that bioq_insert_tail() offers barrier semantic.
Add the BIO_ORDERED flag for struct bio and update bio clients to use it.

The barrier semantics of bioq_insert_tail() were broken in two ways:

 o In bioq_disksort(), an added bio could be inserted at the head of
   the queue, even when a barrier was present, if the sort key for
   the new entry was less than that of the last queued barrier bio.

 o The last_offset used to generate the sort key for newly queued bios
   did not stay at the position of the barrier until either the
   barrier was de-queued, or a new barrier (which updates last_offset)
   was queued.  When a barrier is in effect, we know that the disk
   will pass through the barrier position just before the
   "blocked bios" are released, so using the barrier's offset for
   last_offset is the optimal choice.

sys/geom/sched/subr_disk.c:
sys/kern/subr_disk.c:
	o Update last_offset in bioq_insert_tail().

	o Only update last_offset in bioq_remove() if the removed bio is
	  at the head of the queue (typically due to a call via
	  bioq_takefirst()) and no barrier is active.

	o In bioq_disksort(), if we have a barrier (insert_point is non-NULL),
	  set prev to the barrier and cur to it's next element.  Now that
	  last_offset is kept at the barrier position, this change isn't
	  strictly necessary, but since we have to take a decision branch
	  anyway, it does avoid one, no-op, loop iteration in the while
	  loop that immediately follows.

	o In bioq_disksort(), bypass the normal sort for bios with the
	  BIO_ORDERED attribute and instead insert them into the queue
	  with bioq_insert_tail().  bioq_insert_tail() not only gives
	  the desired command order during insertion, but also provides
	  barrier semantics so that commands disksorted in the future
	  cannot pass the just enqueued transaction.

sys/sys/bio.h:
	Add BIO_ORDERED as bit 4 of the bio_flags field in struct bio.

sys/cam/ata/ata_da.c:
sys/cam/scsi/scsi_da.c
	Use an ordered command for SCSI/ATA-NCQ commands issued in
	response to bios with the BIO_ORDERED flag set.

sys/cam/scsi/scsi_da.c
	Use an ordered tag when issuing a synchronize cache command.

	Wrap some lines to 80 columns.

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
sys/geom/geom_io.c
	Mark bios with the BIO_FLUSH command as BIO_ORDERED.

Sponsored by:	Spectra Logic Corporation
MFC after:	1 month
2010-09-02 19:40:28 +00:00

227 lines
6.5 KiB
C

/*-
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you think
* this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
* ----------------------------------------------------------------------------
*
* The bioq_disksort() (and the specification of the bioq API)
* have been written by Luigi Rizzo and Fabio Checconi under the same
* license as above.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
//#include "opt_geom.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bio.h>
#include <sys/conf.h>
#include <sys/disk.h>
#include <geom/geom_disk.h>
#include "g_sched.h"
/*
* BIO queue implementation
*
* Please read carefully the description below before making any change
* to the code, or you might change the behaviour of the data structure
* in undesirable ways.
*
* A bioq stores disk I/O request (bio), normally sorted according to
* the distance of the requested position (bio->bio_offset) from the
* current head position (bioq->last_offset) in the scan direction, i.e.
*
* (uoff_t)(bio_offset - last_offset)
*
* Note that the cast to unsigned (uoff_t) is fundamental to insure
* that the distance is computed in the scan direction.
*
* The main methods for manipulating the bioq are:
*
* bioq_disksort() performs an ordered insertion;
*
* bioq_first() return the head of the queue, without removing;
*
* bioq_takefirst() return and remove the head of the queue,
* updating the 'current head position' as
* bioq->last_offset = bio->bio_offset + bio->bio_length;
*
* When updating the 'current head position', we assume that the result of
* bioq_takefirst() is dispatched to the device, so bioq->last_offset
* represents the head position once the request is complete.
*
* If the bioq is manipulated using only the above calls, it starts
* with a sorted sequence of requests with bio_offset >= last_offset,
* possibly followed by another sorted sequence of requests with
* 0 <= bio_offset < bioq->last_offset
*
* NOTE: historical behaviour was to ignore bio->bio_length in the
* update, but its use tracks the head position in a better way.
* Historical behaviour was also to update the head position when
* the request under service is complete, rather than when the
* request is extracted from the queue. However, the current API
* has no method to update the head position; secondly, once
* a request has been submitted to the disk, we have no idea of
* the actual head position, so the final one is our best guess.
*
* --- Direct queue manipulation ---
*
* A bioq uses an underlying TAILQ to store requests, so we also
* export methods to manipulate the TAILQ, in particular:
*
* bioq_insert_tail() insert an entry at the end.
* It also creates a 'barrier' so all subsequent
* insertions through bioq_disksort() will end up
* after this entry;
*
* bioq_insert_head() insert an entry at the head, update
* bioq->last_offset = bio->bio_offset so that
* all subsequent insertions through bioq_disksort()
* will end up after this entry;
*
* bioq_remove() remove a generic element from the queue, act as
* bioq_takefirst() if invoked on the head of the queue.
*
* The semantic of these methods is the same as the operations
* on the underlying TAILQ, but with additional guarantees on
* subsequent bioq_disksort() calls. E.g. bioq_insert_tail()
* can be useful for making sure that all previous ops are flushed
* to disk before continuing.
*
* Updating bioq->last_offset on a bioq_insert_head() guarantees
* that the bio inserted with the last bioq_insert_head() will stay
* at the head of the queue even after subsequent bioq_disksort().
*
* Note that when the direct queue manipulation functions are used,
* the queue may contain multiple inversion points (i.e. more than
* two sorted sequences of requests).
*
*/
void
gs_bioq_init(struct bio_queue_head *head)
{
TAILQ_INIT(&head->queue);
head->last_offset = 0;
head->insert_point = NULL;
}
void
gs_bioq_remove(struct bio_queue_head *head, struct bio *bp)
{
if (head->insert_point == NULL) {
if (bp == TAILQ_FIRST(&head->queue))
head->last_offset = bp->bio_offset + bp->bio_length;
} else if (bp == head->insert_point)
head->insert_point = NULL;
TAILQ_REMOVE(&head->queue, bp, bio_queue);
}
void
gs_bioq_flush(struct bio_queue_head *head, struct devstat *stp, int error)
{
struct bio *bp;
while ((bp = gs_bioq_takefirst(head)) != NULL)
biofinish(bp, stp, error);
}
void
gs_bioq_insert_head(struct bio_queue_head *head, struct bio *bp)
{
if (head->insert_point == NULL)
head->last_offset = bp->bio_offset;
TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
}
void
gs_bioq_insert_tail(struct bio_queue_head *head, struct bio *bp)
{
TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue);
head->insert_point = bp;
head->last_offset = bp->bio_offset;
}
struct bio *
gs_bioq_first(struct bio_queue_head *head)
{
return (TAILQ_FIRST(&head->queue));
}
struct bio *
gs_bioq_takefirst(struct bio_queue_head *head)
{
struct bio *bp;
bp = TAILQ_FIRST(&head->queue);
if (bp != NULL)
gs_bioq_remove(head, bp);
return (bp);
}
/*
* Compute the sorting key. The cast to unsigned is
* fundamental for correctness, see the description
* near the beginning of the file.
*/
static inline uoff_t
gs_bioq_bio_key(struct bio_queue_head *head, struct bio *bp)
{
return ((uoff_t)(bp->bio_offset - head->last_offset));
}
/*
* Seek sort for disks.
*
* Sort all requests in a single queue while keeping
* track of the current position of the disk with last_offset.
* See above for details.
*/
void
gs_bioq_disksort(struct bio_queue_head *head, struct bio *bp)
{
struct bio *cur, *prev;
uoff_t key;
if ((bp->bio_flags & BIO_ORDERED) != 0) {
/*
* Ordered transactions can only be dispatched
* after any currently queued transactions. They
* also have barrier semantics - no transactions
* queued in the future can pass them.
*/
gs_bioq_insert_tail(head, bp);
return;
}
prev = NULL;
key = gs_bioq_bio_key(head, bp);
cur = TAILQ_FIRST(&head->queue);
if (head->insert_point) {
prev = head->insert_point;
cur = TAILQ_NEXT(head->insert_point, bio_queue);
}
while (cur != NULL && key >= gs_bioq_bio_key(head, cur)) {
prev = cur;
cur = TAILQ_NEXT(cur, bio_queue);
}
if (prev == NULL)
TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
else
TAILQ_INSERT_AFTER(&head->queue, prev, bp, bio_queue);
}