2 * SPDX-License-Identifier: Beerware
4 * ----------------------------------------------------------------------------
5 * "THE BEER-WARE LICENSE" (Revision 42):
6 * <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
7 * can do whatever you want with this stuff. If we meet some day, and you think
8 * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
9 * ----------------------------------------------------------------------------
11 * The bioq_disksort() (and the specification of the bioq API)
12 * have been written by Luigi Rizzo and Fabio Checconi under the same
16 #include <sys/cdefs.h>
19 #include <sys/param.h>
20 #include <sys/systm.h>
24 #include <sys/sysctl.h>
25 #include <geom/geom_disk.h>
27 static int bioq_batchsize = 128;
28 SYSCTL_INT(_debug, OID_AUTO, bioq_batchsize, CTLFLAG_RW,
29 &bioq_batchsize, 0, "BIOQ batch size");
32 * Disk error is the preface to plaintive error messages
33 * about failing disk transfers. It prints messages of the form
34 * "hp0g: BLABLABLA cmd=read fsbn 12345 of 12344-12347"
35 * blkdone should be -1 if the position of the error is unknown.
36 * The message is printed with printf.
39 disk_err(struct bio *bp, const char *what, int blkdone, int nl)
43 if (bp->bio_dev != NULL)
44 printf("%s: %s ", devtoname(bp->bio_dev), what);
45 else if (bp->bio_disk != NULL)
47 bp->bio_disk->d_name, bp->bio_disk->d_unit, what);
49 printf("disk??: %s ", what);
51 case BIO_READ: printf("cmd=read "); break;
52 case BIO_WRITE: printf("cmd=write "); break;
53 case BIO_DELETE: printf("cmd=delete "); break;
54 case BIO_GETATTR: printf("cmd=getattr "); break;
55 case BIO_FLUSH: printf("cmd=flush "); break;
56 default: printf("cmd=%x ", bp->bio_cmd); break;
59 if (bp->bio_bcount <= DEV_BSIZE) {
60 printf("fsbn %jd%s", (intmax_t)sn, nl ? "\n" : "");
65 printf("fsbn %jd of ", (intmax_t)sn);
67 printf("%jd-%jd", (intmax_t)bp->bio_pblkno,
68 (intmax_t)(bp->bio_pblkno + (bp->bio_bcount - 1) / DEV_BSIZE));
74 * BIO queue implementation
76 * Please read carefully the description below before making any change
77 * to the code, or you might change the behaviour of the data structure
78 * in undesirable ways.
80 * A bioq stores disk I/O request (bio), normally sorted according to
81 * the distance of the requested position (bio->bio_offset) from the
82 * current head position (bioq->last_offset) in the scan direction, i.e.
84 * (uoff_t)(bio_offset - last_offset)
86 * Note that the cast to unsigned (uoff_t) is fundamental to insure
87 * that the distance is computed in the scan direction.
89 * The main methods for manipulating the bioq are:
91 * bioq_disksort() performs an ordered insertion;
93 * bioq_first() return the head of the queue, without removing;
95 * bioq_takefirst() return and remove the head of the queue,
96 * updating the 'current head position' as
97 * bioq->last_offset = bio->bio_offset + bio->bio_length;
99 * When updating the 'current head position', we assume that the result of
100 * bioq_takefirst() is dispatched to the device, so bioq->last_offset
101 * represents the head position once the request is complete.
103 * If the bioq is manipulated using only the above calls, it starts
104 * with a sorted sequence of requests with bio_offset >= last_offset,
105 * possibly followed by another sorted sequence of requests with
106 * 0 <= bio_offset < bioq->last_offset
108 * NOTE: historical behaviour was to ignore bio->bio_length in the
109 * update, but its use tracks the head position in a better way.
110 * Historical behaviour was also to update the head position when
111 * the request under service is complete, rather than when the
112 * request is extracted from the queue. However, the current API
113 * has no method to update the head position; secondly, once
114 * a request has been submitted to the disk, we have no idea of
115 * the actual head position, so the final one is our best guess.
117 * --- Direct queue manipulation ---
119 * A bioq uses an underlying TAILQ to store requests, so we also
120 * export methods to manipulate the TAILQ, in particular:
122 * bioq_insert_tail() insert an entry at the end.
123 * It also creates a 'barrier' so all subsequent
124 * insertions through bioq_disksort() will end up
127 * bioq_insert_head() insert an entry at the head, update
128 * bioq->last_offset = bio->bio_offset so that
129 * all subsequent insertions through bioq_disksort()
130 * will end up after this entry;
132 * bioq_remove() remove a generic element from the queue, act as
133 * bioq_takefirst() if invoked on the head of the queue.
135 * The semantic of these methods is the same as the operations
136 * on the underlying TAILQ, but with additional guarantees on
137 * subsequent bioq_disksort() calls. E.g. bioq_insert_tail()
138 * can be useful for making sure that all previous ops are flushed
139 * to disk before continuing.
141 * Updating bioq->last_offset on a bioq_insert_head() guarantees
142 * that the bio inserted with the last bioq_insert_head() will stay
143 * at the head of the queue even after subsequent bioq_disksort().
145 * Note that when the direct queue manipulation functions are used,
146 * the queue may contain multiple inversion points (i.e. more than
147 * two sorted sequences of requests).
152 bioq_init(struct bio_queue_head *head)
155 TAILQ_INIT(&head->queue);
156 head->last_offset = 0;
157 head->insert_point = NULL;
163 bioq_remove(struct bio_queue_head *head, struct bio *bp)
166 if (head->insert_point == NULL) {
167 if (bp == TAILQ_FIRST(&head->queue))
168 head->last_offset = bp->bio_offset + bp->bio_length;
169 } else if (bp == head->insert_point)
170 head->insert_point = NULL;
172 TAILQ_REMOVE(&head->queue, bp, bio_queue);
173 if (TAILQ_EMPTY(&head->queue))
179 bioq_flush(struct bio_queue_head *head, struct devstat *stp, int error)
183 while ((bp = bioq_takefirst(head)) != NULL)
184 biofinish(bp, stp, error);
188 bioq_insert_head(struct bio_queue_head *head, struct bio *bp)
191 if (head->insert_point == NULL)
192 head->last_offset = bp->bio_offset;
193 TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
199 bioq_insert_tail(struct bio_queue_head *head, struct bio *bp)
202 TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue);
205 head->insert_point = bp;
206 head->last_offset = bp->bio_offset;
210 bioq_first(struct bio_queue_head *head)
213 return (TAILQ_FIRST(&head->queue));
217 bioq_takefirst(struct bio_queue_head *head)
221 bp = TAILQ_FIRST(&head->queue);
223 bioq_remove(head, bp);
228 * Compute the sorting key. The cast to unsigned is
229 * fundamental for correctness, see the description
230 * near the beginning of the file.
233 bioq_bio_key(struct bio_queue_head *head, struct bio *bp)
236 return ((uoff_t)(bp->bio_offset - head->last_offset));
240 * Seek sort for disks.
242 * Sort all requests in a single queue while keeping
243 * track of the current position of the disk with last_offset.
244 * See above for details.
247 bioq_disksort(struct bio_queue_head *head, struct bio *bp)
249 struct bio *cur, *prev;
252 if ((bp->bio_flags & BIO_ORDERED) != 0) {
254 * Ordered transactions can only be dispatched
255 * after any currently queued transactions. They
256 * also have barrier semantics - no transactions
257 * queued in the future can pass them.
259 bioq_insert_tail(head, bp);
264 * We should only sort requests of types that have concept of offset.
265 * Other types, such as BIO_FLUSH or BIO_ZONE, may imply some degree
266 * of ordering even if strict ordering is not requested explicitly.
268 if (bp->bio_cmd != BIO_READ && bp->bio_cmd != BIO_WRITE &&
269 bp->bio_cmd != BIO_DELETE) {
270 bioq_insert_tail(head, bp);
274 if (bioq_batchsize > 0 && head->batched > bioq_batchsize) {
275 bioq_insert_tail(head, bp);
280 key = bioq_bio_key(head, bp);
281 cur = TAILQ_FIRST(&head->queue);
283 if (head->insert_point) {
284 prev = head->insert_point;
285 cur = TAILQ_NEXT(head->insert_point, bio_queue);
288 while (cur != NULL && key >= bioq_bio_key(head, cur)) {
290 cur = TAILQ_NEXT(cur, bio_queue);
294 TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
296 TAILQ_INSERT_AFTER(&head->queue, prev, bp, bio_queue);