Root/block/deadline-iosched.c

1/*
2 * Deadline i/o scheduler.
3 *
4 * Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
5 */
6#include <linux/kernel.h>
7#include <linux/fs.h>
8#include <linux/blkdev.h>
9#include <linux/elevator.h>
10#include <linux/bio.h>
11#include <linux/module.h>
12#include <linux/slab.h>
13#include <linux/init.h>
14#include <linux/compiler.h>
15#include <linux/rbtree.h>
16
17/*
18 * See Documentation/block/deadline-iosched.txt
19 */
20static const int read_expire = HZ / 2; /* max time before a read is submitted. */
21static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
22static const int writes_starved = 2; /* max times reads can starve a write */
23static const int fifo_batch = 16; /* # of sequential requests treated as one
24                     by the above parameters. For throughput. */
25
26struct deadline_data {
27    /*
28     * run time data
29     */
30
31    /*
32     * requests (deadline_rq s) are present on both sort_list and fifo_list
33     */
34    struct rb_root sort_list[2];
35    struct list_head fifo_list[2];
36
37    /*
38     * next in sort order. read, write or both are NULL
39     */
40    struct request *next_rq[2];
41    unsigned int batching; /* number of sequential requests made */
42    sector_t last_sector; /* head position */
43    unsigned int starved; /* times reads have starved writes */
44
45    /*
46     * settings that change how the i/o scheduler behaves
47     */
48    int fifo_expire[2];
49    int fifo_batch;
50    int writes_starved;
51    int front_merges;
52};
53
54static void deadline_move_request(struct deadline_data *, struct request *);
55
56static inline struct rb_root *
57deadline_rb_root(struct deadline_data *dd, struct request *rq)
58{
59    return &dd->sort_list[rq_data_dir(rq)];
60}
61
62/*
63 * get the request after `rq' in sector-sorted order
64 */
65static inline struct request *
66deadline_latter_request(struct request *rq)
67{
68    struct rb_node *node = rb_next(&rq->rb_node);
69
70    if (node)
71        return rb_entry_rq(node);
72
73    return NULL;
74}
75
76static void
77deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
78{
79    struct rb_root *root = deadline_rb_root(dd, rq);
80
81    elv_rb_add(root, rq);
82}
83
84static inline void
85deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
86{
87    const int data_dir = rq_data_dir(rq);
88
89    if (dd->next_rq[data_dir] == rq)
90        dd->next_rq[data_dir] = deadline_latter_request(rq);
91
92    elv_rb_del(deadline_rb_root(dd, rq), rq);
93}
94
95/*
96 * add rq to rbtree and fifo
97 */
98static void
99deadline_add_request(struct request_queue *q, struct request *rq)
100{
101    struct deadline_data *dd = q->elevator->elevator_data;
102    const int data_dir = rq_data_dir(rq);
103
104    deadline_add_rq_rb(dd, rq);
105
106    /*
107     * set expire time and add to fifo list
108     */
109    rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
110    list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
111}
112
113/*
114 * remove rq from rbtree and fifo.
115 */
116static void deadline_remove_request(struct request_queue *q, struct request *rq)
117{
118    struct deadline_data *dd = q->elevator->elevator_data;
119
120    rq_fifo_clear(rq);
121    deadline_del_rq_rb(dd, rq);
122}
123
124static int
125deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
126{
127    struct deadline_data *dd = q->elevator->elevator_data;
128    struct request *__rq;
129    int ret;
130
131    /*
132     * check for front merge
133     */
134    if (dd->front_merges) {
135        sector_t sector = bio_end_sector(bio);
136
137        __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
138        if (__rq) {
139            BUG_ON(sector != blk_rq_pos(__rq));
140
141            if (elv_rq_merge_ok(__rq, bio)) {
142                ret = ELEVATOR_FRONT_MERGE;
143                goto out;
144            }
145        }
146    }
147
148    return ELEVATOR_NO_MERGE;
149out:
150    *req = __rq;
151    return ret;
152}
153
154static void deadline_merged_request(struct request_queue *q,
155                    struct request *req, int type)
156{
157    struct deadline_data *dd = q->elevator->elevator_data;
158
159    /*
160     * if the merge was a front merge, we need to reposition request
161     */
162    if (type == ELEVATOR_FRONT_MERGE) {
163        elv_rb_del(deadline_rb_root(dd, req), req);
164        deadline_add_rq_rb(dd, req);
165    }
166}
167
168static void
169deadline_merged_requests(struct request_queue *q, struct request *req,
170             struct request *next)
171{
172    /*
173     * if next expires before rq, assign its expire time to rq
174     * and move into next position (next will be deleted) in fifo
175     */
176    if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
177        if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
178            list_move(&req->queuelist, &next->queuelist);
179            rq_set_fifo_time(req, rq_fifo_time(next));
180        }
181    }
182
183    /*
184     * kill knowledge of next, this one is a goner
185     */
186    deadline_remove_request(q, next);
187}
188
189/*
190 * move request from sort list to dispatch queue.
191 */
192static inline void
193deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
194{
195    struct request_queue *q = rq->q;
196
197    deadline_remove_request(q, rq);
198    elv_dispatch_add_tail(q, rq);
199}
200
201/*
202 * move an entry to dispatch queue
203 */
204static void
205deadline_move_request(struct deadline_data *dd, struct request *rq)
206{
207    const int data_dir = rq_data_dir(rq);
208
209    dd->next_rq[READ] = NULL;
210    dd->next_rq[WRITE] = NULL;
211    dd->next_rq[data_dir] = deadline_latter_request(rq);
212
213    dd->last_sector = rq_end_sector(rq);
214
215    /*
216     * take it off the sort and fifo list, move
217     * to dispatch queue
218     */
219    deadline_move_to_dispatch(dd, rq);
220}
221
222/*
223 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
224 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
225 */
226static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
227{
228    struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
229
230    /*
231     * rq is expired!
232     */
233    if (time_after_eq(jiffies, rq_fifo_time(rq)))
234        return 1;
235
236    return 0;
237}
238
239/*
240 * deadline_dispatch_requests selects the best request according to
241 * read/write expire, fifo_batch, etc
242 */
243static int deadline_dispatch_requests(struct request_queue *q, int force)
244{
245    struct deadline_data *dd = q->elevator->elevator_data;
246    const int reads = !list_empty(&dd->fifo_list[READ]);
247    const int writes = !list_empty(&dd->fifo_list[WRITE]);
248    struct request *rq;
249    int data_dir;
250
251    /*
252     * batches are currently reads XOR writes
253     */
254    if (dd->next_rq[WRITE])
255        rq = dd->next_rq[WRITE];
256    else
257        rq = dd->next_rq[READ];
258
259    if (rq && dd->batching < dd->fifo_batch)
260        /* we have a next request are still entitled to batch */
261        goto dispatch_request;
262
263    /*
264     * at this point we are not running a batch. select the appropriate
265     * data direction (read / write)
266     */
267
268    if (reads) {
269        BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
270
271        if (writes && (dd->starved++ >= dd->writes_starved))
272            goto dispatch_writes;
273
274        data_dir = READ;
275
276        goto dispatch_find_request;
277    }
278
279    /*
280     * there are either no reads or writes have been starved
281     */
282
283    if (writes) {
284dispatch_writes:
285        BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
286
287        dd->starved = 0;
288
289        data_dir = WRITE;
290
291        goto dispatch_find_request;
292    }
293
294    return 0;
295
296dispatch_find_request:
297    /*
298     * we are not running a batch, find best request for selected data_dir
299     */
300    if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
301        /*
302         * A deadline has expired, the last request was in the other
303         * direction, or we have run out of higher-sectored requests.
304         * Start again from the request with the earliest expiry time.
305         */
306        rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
307    } else {
308        /*
309         * The last req was the same dir and we have a next request in
310         * sort order. No expired requests so continue on from here.
311         */
312        rq = dd->next_rq[data_dir];
313    }
314
315    dd->batching = 0;
316
317dispatch_request:
318    /*
319     * rq is the selected appropriate request.
320     */
321    dd->batching++;
322    deadline_move_request(dd, rq);
323
324    return 1;
325}
326
327static void deadline_exit_queue(struct elevator_queue *e)
328{
329    struct deadline_data *dd = e->elevator_data;
330
331    BUG_ON(!list_empty(&dd->fifo_list[READ]));
332    BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
333
334    kfree(dd);
335}
336
337/*
338 * initialize elevator private data (deadline_data).
339 */
340static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
341{
342    struct deadline_data *dd;
343    struct elevator_queue *eq;
344
345    eq = elevator_alloc(q, e);
346    if (!eq)
347        return -ENOMEM;
348
349    dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
350    if (!dd) {
351        kobject_put(&eq->kobj);
352        return -ENOMEM;
353    }
354    eq->elevator_data = dd;
355
356    INIT_LIST_HEAD(&dd->fifo_list[READ]);
357    INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
358    dd->sort_list[READ] = RB_ROOT;
359    dd->sort_list[WRITE] = RB_ROOT;
360    dd->fifo_expire[READ] = read_expire;
361    dd->fifo_expire[WRITE] = write_expire;
362    dd->writes_starved = writes_starved;
363    dd->front_merges = 1;
364    dd->fifo_batch = fifo_batch;
365
366    spin_lock_irq(q->queue_lock);
367    q->elevator = eq;
368    spin_unlock_irq(q->queue_lock);
369    return 0;
370}
371
372/*
373 * sysfs parts below
374 */
375
376static ssize_t
377deadline_var_show(int var, char *page)
378{
379    return sprintf(page, "%d\n", var);
380}
381
382static ssize_t
383deadline_var_store(int *var, const char *page, size_t count)
384{
385    char *p = (char *) page;
386
387    *var = simple_strtol(p, &p, 10);
388    return count;
389}
390
391#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
392static ssize_t __FUNC(struct elevator_queue *e, char *page) \
393{ \
394    struct deadline_data *dd = e->elevator_data; \
395    int __data = __VAR; \
396    if (__CONV) \
397        __data = jiffies_to_msecs(__data); \
398    return deadline_var_show(__data, (page)); \
399}
400SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
401SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
402SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
403SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
404SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
405#undef SHOW_FUNCTION
406
407#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
408static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
409{ \
410    struct deadline_data *dd = e->elevator_data; \
411    int __data; \
412    int ret = deadline_var_store(&__data, (page), count); \
413    if (__data < (MIN)) \
414        __data = (MIN); \
415    else if (__data > (MAX)) \
416        __data = (MAX); \
417    if (__CONV) \
418        *(__PTR) = msecs_to_jiffies(__data); \
419    else \
420        *(__PTR) = __data; \
421    return ret; \
422}
423STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
424STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
425STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
426STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
427STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
428#undef STORE_FUNCTION
429
430#define DD_ATTR(name) \
431    __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
432                      deadline_##name##_store)
433
434static struct elv_fs_entry deadline_attrs[] = {
435    DD_ATTR(read_expire),
436    DD_ATTR(write_expire),
437    DD_ATTR(writes_starved),
438    DD_ATTR(front_merges),
439    DD_ATTR(fifo_batch),
440    __ATTR_NULL
441};
442
443static struct elevator_type iosched_deadline = {
444    .ops = {
445        .elevator_merge_fn = deadline_merge,
446        .elevator_merged_fn = deadline_merged_request,
447        .elevator_merge_req_fn = deadline_merged_requests,
448        .elevator_dispatch_fn = deadline_dispatch_requests,
449        .elevator_add_req_fn = deadline_add_request,
450        .elevator_former_req_fn = elv_rb_former_request,
451        .elevator_latter_req_fn = elv_rb_latter_request,
452        .elevator_init_fn = deadline_init_queue,
453        .elevator_exit_fn = deadline_exit_queue,
454    },
455
456    .elevator_attrs = deadline_attrs,
457    .elevator_name = "deadline",
458    .elevator_owner = THIS_MODULE,
459};
460
461static int __init deadline_init(void)
462{
463    return elv_register(&iosched_deadline);
464}
465
466static void __exit deadline_exit(void)
467{
468    elv_unregister(&iosched_deadline);
469}
470
471module_init(deadline_init);
472module_exit(deadline_exit);
473
474MODULE_AUTHOR("Jens Axboe");
475MODULE_LICENSE("GPL");
476MODULE_DESCRIPTION("deadline IO scheduler");
477

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