linux/block/deadline-iosched.c

813 lines
19 KiB
C

/*
* Deadline i/o scheduler.
*
* Copyright (C) 2002 Jens Axboe <axboe@suse.de>
*/
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/hash.h>
#include <linux/rbtree.h>
/*
* See Documentation/block/deadline-iosched.txt
*/
static const int read_expire = HZ / 2; /* max time before a read is submitted. */
static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
static const int writes_starved = 2; /* max times reads can starve a write */
static const int fifo_batch = 16; /* # of sequential requests treated as one
by the above parameters. For throughput. */
static const int deadline_hash_shift = 5;
#define DL_HASH_BLOCK(sec) ((sec) >> 3)
#define DL_HASH_FN(sec) (hash_long(DL_HASH_BLOCK((sec)), deadline_hash_shift))
#define DL_HASH_ENTRIES (1 << deadline_hash_shift)
#define rq_hash_key(rq) ((rq)->sector + (rq)->nr_sectors)
#define list_entry_hash(ptr) list_entry((ptr), struct deadline_rq, hash)
#define ON_HASH(drq) (drq)->on_hash
struct deadline_data {
/*
* run time data
*/
/*
* requests (deadline_rq s) are present on both sort_list and fifo_list
*/
struct rb_root sort_list[2];
struct list_head fifo_list[2];
/*
* next in sort order. read, write or both are NULL
*/
struct deadline_rq *next_drq[2];
struct list_head *hash; /* request hash */
unsigned int batching; /* number of sequential requests made */
sector_t last_sector; /* head position */
unsigned int starved; /* times reads have starved writes */
/*
* settings that change how the i/o scheduler behaves
*/
int fifo_expire[2];
int fifo_batch;
int writes_starved;
int front_merges;
mempool_t *drq_pool;
};
/*
* pre-request data.
*/
struct deadline_rq {
/*
* rbtree index, key is the starting offset
*/
struct rb_node rb_node;
sector_t rb_key;
struct request *request;
/*
* request hash, key is the ending offset (for back merge lookup)
*/
struct list_head hash;
char on_hash;
/*
* expire fifo
*/
struct list_head fifo;
unsigned long expires;
};
static void deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq);
static kmem_cache_t *drq_pool;
#define RQ_DATA(rq) ((struct deadline_rq *) (rq)->elevator_private)
/*
* the back merge hash support functions
*/
static inline void __deadline_del_drq_hash(struct deadline_rq *drq)
{
drq->on_hash = 0;
list_del_init(&drq->hash);
}
static inline void deadline_del_drq_hash(struct deadline_rq *drq)
{
if (ON_HASH(drq))
__deadline_del_drq_hash(drq);
}
static inline void
deadline_add_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
{
struct request *rq = drq->request;
BUG_ON(ON_HASH(drq));
drq->on_hash = 1;
list_add(&drq->hash, &dd->hash[DL_HASH_FN(rq_hash_key(rq))]);
}
/*
* move hot entry to front of chain
*/
static inline void
deadline_hot_drq_hash(struct deadline_data *dd, struct deadline_rq *drq)
{
struct request *rq = drq->request;
struct list_head *head = &dd->hash[DL_HASH_FN(rq_hash_key(rq))];
if (ON_HASH(drq) && drq->hash.prev != head) {
list_del(&drq->hash);
list_add(&drq->hash, head);
}
}
static struct request *
deadline_find_drq_hash(struct deadline_data *dd, sector_t offset)
{
struct list_head *hash_list = &dd->hash[DL_HASH_FN(offset)];
struct list_head *entry, *next = hash_list->next;
while ((entry = next) != hash_list) {
struct deadline_rq *drq = list_entry_hash(entry);
struct request *__rq = drq->request;
next = entry->next;
BUG_ON(!ON_HASH(drq));
if (!rq_mergeable(__rq)) {
__deadline_del_drq_hash(drq);
continue;
}
if (rq_hash_key(__rq) == offset)
return __rq;
}
return NULL;
}
/*
* rb tree support functions
*/
#define RB_EMPTY(root) ((root)->rb_node == NULL)
#define ON_RB(node) (rb_parent(node) != node)
#define RB_CLEAR(node) (rb_set_parent(node, node))
#define rb_entry_drq(node) rb_entry((node), struct deadline_rq, rb_node)
#define DRQ_RB_ROOT(dd, drq) (&(dd)->sort_list[rq_data_dir((drq)->request)])
#define rq_rb_key(rq) (rq)->sector
static struct deadline_rq *
__deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
struct rb_node **p = &DRQ_RB_ROOT(dd, drq)->rb_node;
struct rb_node *parent = NULL;
struct deadline_rq *__drq;
while (*p) {
parent = *p;
__drq = rb_entry_drq(parent);
if (drq->rb_key < __drq->rb_key)
p = &(*p)->rb_left;
else if (drq->rb_key > __drq->rb_key)
p = &(*p)->rb_right;
else
return __drq;
}
rb_link_node(&drq->rb_node, parent, p);
return NULL;
}
static void
deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
struct deadline_rq *__alias;
drq->rb_key = rq_rb_key(drq->request);
retry:
__alias = __deadline_add_drq_rb(dd, drq);
if (!__alias) {
rb_insert_color(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
return;
}
deadline_move_request(dd, __alias);
goto retry;
}
static inline void
deadline_del_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
{
const int data_dir = rq_data_dir(drq->request);
if (dd->next_drq[data_dir] == drq) {
struct rb_node *rbnext = rb_next(&drq->rb_node);
dd->next_drq[data_dir] = NULL;
if (rbnext)
dd->next_drq[data_dir] = rb_entry_drq(rbnext);
}
BUG_ON(!ON_RB(&drq->rb_node));
rb_erase(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
RB_CLEAR(&drq->rb_node);
}
static struct request *
deadline_find_drq_rb(struct deadline_data *dd, sector_t sector, int data_dir)
{
struct rb_node *n = dd->sort_list[data_dir].rb_node;
struct deadline_rq *drq;
while (n) {
drq = rb_entry_drq(n);
if (sector < drq->rb_key)
n = n->rb_left;
else if (sector > drq->rb_key)
n = n->rb_right;
else
return drq->request;
}
return NULL;
}
/*
* deadline_find_first_drq finds the first (lowest sector numbered) request
* for the specified data_dir. Used to sweep back to the start of the disk
* (1-way elevator) after we process the last (highest sector) request.
*/
static struct deadline_rq *
deadline_find_first_drq(struct deadline_data *dd, int data_dir)
{
struct rb_node *n = dd->sort_list[data_dir].rb_node;
for (;;) {
if (n->rb_left == NULL)
return rb_entry_drq(n);
n = n->rb_left;
}
}
/*
* add drq to rbtree and fifo
*/
static void
deadline_add_request(struct request_queue *q, struct request *rq)
{
struct deadline_data *dd = q->elevator->elevator_data;
struct deadline_rq *drq = RQ_DATA(rq);
const int data_dir = rq_data_dir(drq->request);
deadline_add_drq_rb(dd, drq);
/*
* set expire time (only used for reads) and add to fifo list
*/
drq->expires = jiffies + dd->fifo_expire[data_dir];
list_add_tail(&drq->fifo, &dd->fifo_list[data_dir]);
if (rq_mergeable(rq))
deadline_add_drq_hash(dd, drq);
}
/*
* remove rq from rbtree, fifo, and hash
*/
static void deadline_remove_request(request_queue_t *q, struct request *rq)
{
struct deadline_rq *drq = RQ_DATA(rq);
struct deadline_data *dd = q->elevator->elevator_data;
list_del_init(&drq->fifo);
deadline_del_drq_rb(dd, drq);
deadline_del_drq_hash(drq);
}
static int
deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
struct deadline_data *dd = q->elevator->elevator_data;
struct request *__rq;
int ret;
/*
* see if the merge hash can satisfy a back merge
*/
__rq = deadline_find_drq_hash(dd, bio->bi_sector);
if (__rq) {
BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector);
if (elv_rq_merge_ok(__rq, bio)) {
ret = ELEVATOR_BACK_MERGE;
goto out;
}
}
/*
* check for front merge
*/
if (dd->front_merges) {
sector_t rb_key = bio->bi_sector + bio_sectors(bio);
__rq = deadline_find_drq_rb(dd, rb_key, bio_data_dir(bio));
if (__rq) {
BUG_ON(rb_key != rq_rb_key(__rq));
if (elv_rq_merge_ok(__rq, bio)) {
ret = ELEVATOR_FRONT_MERGE;
goto out;
}
}
}
return ELEVATOR_NO_MERGE;
out:
if (ret)
deadline_hot_drq_hash(dd, RQ_DATA(__rq));
*req = __rq;
return ret;
}
static void deadline_merged_request(request_queue_t *q, struct request *req)
{
struct deadline_data *dd = q->elevator->elevator_data;
struct deadline_rq *drq = RQ_DATA(req);
/*
* hash always needs to be repositioned, key is end sector
*/
deadline_del_drq_hash(drq);
deadline_add_drq_hash(dd, drq);
/*
* if the merge was a front merge, we need to reposition request
*/
if (rq_rb_key(req) != drq->rb_key) {
deadline_del_drq_rb(dd, drq);
deadline_add_drq_rb(dd, drq);
}
}
static void
deadline_merged_requests(request_queue_t *q, struct request *req,
struct request *next)
{
struct deadline_data *dd = q->elevator->elevator_data;
struct deadline_rq *drq = RQ_DATA(req);
struct deadline_rq *dnext = RQ_DATA(next);
BUG_ON(!drq);
BUG_ON(!dnext);
/*
* reposition drq (this is the merged request) in hash, and in rbtree
* in case of a front merge
*/
deadline_del_drq_hash(drq);
deadline_add_drq_hash(dd, drq);
if (rq_rb_key(req) != drq->rb_key) {
deadline_del_drq_rb(dd, drq);
deadline_add_drq_rb(dd, drq);
}
/*
* if dnext expires before drq, assign its expire time to drq
* and move into dnext position (dnext will be deleted) in fifo
*/
if (!list_empty(&drq->fifo) && !list_empty(&dnext->fifo)) {
if (time_before(dnext->expires, drq->expires)) {
list_move(&drq->fifo, &dnext->fifo);
drq->expires = dnext->expires;
}
}
/*
* kill knowledge of next, this one is a goner
*/
deadline_remove_request(q, next);
}
/*
* move request from sort list to dispatch queue.
*/
static inline void
deadline_move_to_dispatch(struct deadline_data *dd, struct deadline_rq *drq)
{
request_queue_t *q = drq->request->q;
deadline_remove_request(q, drq->request);
elv_dispatch_add_tail(q, drq->request);
}
/*
* move an entry to dispatch queue
*/
static void
deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq)
{
const int data_dir = rq_data_dir(drq->request);
struct rb_node *rbnext = rb_next(&drq->rb_node);
dd->next_drq[READ] = NULL;
dd->next_drq[WRITE] = NULL;
if (rbnext)
dd->next_drq[data_dir] = rb_entry_drq(rbnext);
dd->last_sector = drq->request->sector + drq->request->nr_sectors;
/*
* take it off the sort and fifo list, move
* to dispatch queue
*/
deadline_move_to_dispatch(dd, drq);
}
#define list_entry_fifo(ptr) list_entry((ptr), struct deadline_rq, fifo)
/*
* deadline_check_fifo returns 0 if there are no expired reads on the fifo,
* 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
*/
static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
{
struct deadline_rq *drq = list_entry_fifo(dd->fifo_list[ddir].next);
/*
* drq is expired!
*/
if (time_after(jiffies, drq->expires))
return 1;
return 0;
}
/*
* deadline_dispatch_requests selects the best request according to
* read/write expire, fifo_batch, etc
*/
static int deadline_dispatch_requests(request_queue_t *q, int force)
{
struct deadline_data *dd = q->elevator->elevator_data;
const int reads = !list_empty(&dd->fifo_list[READ]);
const int writes = !list_empty(&dd->fifo_list[WRITE]);
struct deadline_rq *drq;
int data_dir;
/*
* batches are currently reads XOR writes
*/
if (dd->next_drq[WRITE])
drq = dd->next_drq[WRITE];
else
drq = dd->next_drq[READ];
if (drq) {
/* we have a "next request" */
if (dd->last_sector != drq->request->sector)
/* end the batch on a non sequential request */
dd->batching += dd->fifo_batch;
if (dd->batching < dd->fifo_batch)
/* we are still entitled to batch */
goto dispatch_request;
}
/*
* at this point we are not running a batch. select the appropriate
* data direction (read / write)
*/
if (reads) {
BUG_ON(RB_EMPTY(&dd->sort_list[READ]));
if (writes && (dd->starved++ >= dd->writes_starved))
goto dispatch_writes;
data_dir = READ;
goto dispatch_find_request;
}
/*
* there are either no reads or writes have been starved
*/
if (writes) {
dispatch_writes:
BUG_ON(RB_EMPTY(&dd->sort_list[WRITE]));
dd->starved = 0;
data_dir = WRITE;
goto dispatch_find_request;
}
return 0;
dispatch_find_request:
/*
* we are not running a batch, find best request for selected data_dir
*/
if (deadline_check_fifo(dd, data_dir)) {
/* An expired request exists - satisfy it */
dd->batching = 0;
drq = list_entry_fifo(dd->fifo_list[data_dir].next);
} else if (dd->next_drq[data_dir]) {
/*
* The last req was the same dir and we have a next request in
* sort order. No expired requests so continue on from here.
*/
drq = dd->next_drq[data_dir];
} else {
/*
* The last req was the other direction or we have run out of
* higher-sectored requests. Go back to the lowest sectored
* request (1 way elevator) and start a new batch.
*/
dd->batching = 0;
drq = deadline_find_first_drq(dd, data_dir);
}
dispatch_request:
/*
* drq is the selected appropriate request.
*/
dd->batching++;
deadline_move_request(dd, drq);
return 1;
}
static int deadline_queue_empty(request_queue_t *q)
{
struct deadline_data *dd = q->elevator->elevator_data;
return list_empty(&dd->fifo_list[WRITE])
&& list_empty(&dd->fifo_list[READ]);
}
static struct request *
deadline_former_request(request_queue_t *q, struct request *rq)
{
struct deadline_rq *drq = RQ_DATA(rq);
struct rb_node *rbprev = rb_prev(&drq->rb_node);
if (rbprev)
return rb_entry_drq(rbprev)->request;
return NULL;
}
static struct request *
deadline_latter_request(request_queue_t *q, struct request *rq)
{
struct deadline_rq *drq = RQ_DATA(rq);
struct rb_node *rbnext = rb_next(&drq->rb_node);
if (rbnext)
return rb_entry_drq(rbnext)->request;
return NULL;
}
static void deadline_exit_queue(elevator_t *e)
{
struct deadline_data *dd = e->elevator_data;
BUG_ON(!list_empty(&dd->fifo_list[READ]));
BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
mempool_destroy(dd->drq_pool);
kfree(dd->hash);
kfree(dd);
}
/*
* initialize elevator private data (deadline_data), and alloc a drq for
* each request on the free lists
*/
static void *deadline_init_queue(request_queue_t *q, elevator_t *e)
{
struct deadline_data *dd;
int i;
if (!drq_pool)
return NULL;
dd = kmalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
if (!dd)
return NULL;
memset(dd, 0, sizeof(*dd));
dd->hash = kmalloc_node(sizeof(struct list_head)*DL_HASH_ENTRIES,
GFP_KERNEL, q->node);
if (!dd->hash) {
kfree(dd);
return NULL;
}
dd->drq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
mempool_free_slab, drq_pool, q->node);
if (!dd->drq_pool) {
kfree(dd->hash);
kfree(dd);
return NULL;
}
for (i = 0; i < DL_HASH_ENTRIES; i++)
INIT_LIST_HEAD(&dd->hash[i]);
INIT_LIST_HEAD(&dd->fifo_list[READ]);
INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
dd->sort_list[READ] = RB_ROOT;
dd->sort_list[WRITE] = RB_ROOT;
dd->fifo_expire[READ] = read_expire;
dd->fifo_expire[WRITE] = write_expire;
dd->writes_starved = writes_starved;
dd->front_merges = 1;
dd->fifo_batch = fifo_batch;
return dd;
}
static void deadline_put_request(request_queue_t *q, struct request *rq)
{
struct deadline_data *dd = q->elevator->elevator_data;
struct deadline_rq *drq = RQ_DATA(rq);
mempool_free(drq, dd->drq_pool);
rq->elevator_private = NULL;
}
static int
deadline_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
gfp_t gfp_mask)
{
struct deadline_data *dd = q->elevator->elevator_data;
struct deadline_rq *drq;
drq = mempool_alloc(dd->drq_pool, gfp_mask);
if (drq) {
memset(drq, 0, sizeof(*drq));
RB_CLEAR(&drq->rb_node);
drq->request = rq;
INIT_LIST_HEAD(&drq->hash);
drq->on_hash = 0;
INIT_LIST_HEAD(&drq->fifo);
rq->elevator_private = drq;
return 0;
}
return 1;
}
/*
* sysfs parts below
*/
static ssize_t
deadline_var_show(int var, char *page)
{
return sprintf(page, "%d\n", var);
}
static ssize_t
deadline_var_store(int *var, const char *page, size_t count)
{
char *p = (char *) page;
*var = simple_strtol(p, &p, 10);
return count;
}
#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
static ssize_t __FUNC(elevator_t *e, char *page) \
{ \
struct deadline_data *dd = e->elevator_data; \
int __data = __VAR; \
if (__CONV) \
__data = jiffies_to_msecs(__data); \
return deadline_var_show(__data, (page)); \
}
SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
#undef SHOW_FUNCTION
#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
static ssize_t __FUNC(elevator_t *e, const char *page, size_t count) \
{ \
struct deadline_data *dd = e->elevator_data; \
int __data; \
int ret = deadline_var_store(&__data, (page), count); \
if (__data < (MIN)) \
__data = (MIN); \
else if (__data > (MAX)) \
__data = (MAX); \
if (__CONV) \
*(__PTR) = msecs_to_jiffies(__data); \
else \
*(__PTR) = __data; \
return ret; \
}
STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
#undef STORE_FUNCTION
#define DD_ATTR(name) \
__ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
deadline_##name##_store)
static struct elv_fs_entry deadline_attrs[] = {
DD_ATTR(read_expire),
DD_ATTR(write_expire),
DD_ATTR(writes_starved),
DD_ATTR(front_merges),
DD_ATTR(fifo_batch),
__ATTR_NULL
};
static struct elevator_type iosched_deadline = {
.ops = {
.elevator_merge_fn = deadline_merge,
.elevator_merged_fn = deadline_merged_request,
.elevator_merge_req_fn = deadline_merged_requests,
.elevator_dispatch_fn = deadline_dispatch_requests,
.elevator_add_req_fn = deadline_add_request,
.elevator_queue_empty_fn = deadline_queue_empty,
.elevator_former_req_fn = deadline_former_request,
.elevator_latter_req_fn = deadline_latter_request,
.elevator_set_req_fn = deadline_set_request,
.elevator_put_req_fn = deadline_put_request,
.elevator_init_fn = deadline_init_queue,
.elevator_exit_fn = deadline_exit_queue,
},
.elevator_attrs = deadline_attrs,
.elevator_name = "deadline",
.elevator_owner = THIS_MODULE,
};
static int __init deadline_init(void)
{
int ret;
drq_pool = kmem_cache_create("deadline_drq", sizeof(struct deadline_rq),
0, 0, NULL, NULL);
if (!drq_pool)
return -ENOMEM;
ret = elv_register(&iosched_deadline);
if (ret)
kmem_cache_destroy(drq_pool);
return ret;
}
static void __exit deadline_exit(void)
{
kmem_cache_destroy(drq_pool);
elv_unregister(&iosched_deadline);
}
module_init(deadline_init);
module_exit(deadline_exit);
MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("deadline IO scheduler");