6f5d8aa638
After switching data directions, deadline always starts the next batch from the lowest-sector request. This gives excessive deadline expiries and large latency and throughput disparity between high- and low-sector requests; an order of magnitude in some tests. This patch changes the batching behaviour so new batches start from the request whose expiry is earliest. Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
483 lines
12 KiB
C
483 lines
12 KiB
C
/*
|
|
* Deadline i/o scheduler.
|
|
*
|
|
* Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
|
|
*/
|
|
#include <linux/kernel.h>
|
|
#include <linux/fs.h>
|
|
#include <linux/blkdev.h>
|
|
#include <linux/elevator.h>
|
|
#include <linux/bio.h>
|
|
#include <linux/module.h>
|
|
#include <linux/slab.h>
|
|
#include <linux/init.h>
|
|
#include <linux/compiler.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. */
|
|
|
|
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 request *next_rq[2];
|
|
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;
|
|
};
|
|
|
|
static void deadline_move_request(struct deadline_data *, struct request *);
|
|
|
|
#define RQ_RB_ROOT(dd, rq) (&(dd)->sort_list[rq_data_dir((rq))])
|
|
|
|
/*
|
|
* get the request after `rq' in sector-sorted order
|
|
*/
|
|
static inline struct request *
|
|
deadline_latter_request(struct request *rq)
|
|
{
|
|
struct rb_node *node = rb_next(&rq->rb_node);
|
|
|
|
if (node)
|
|
return rb_entry_rq(node);
|
|
|
|
return NULL;
|
|
}
|
|
|
|
static void
|
|
deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
|
|
{
|
|
struct rb_root *root = RQ_RB_ROOT(dd, rq);
|
|
struct request *__alias;
|
|
|
|
retry:
|
|
__alias = elv_rb_add(root, rq);
|
|
if (unlikely(__alias)) {
|
|
deadline_move_request(dd, __alias);
|
|
goto retry;
|
|
}
|
|
}
|
|
|
|
static inline void
|
|
deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
|
|
{
|
|
const int data_dir = rq_data_dir(rq);
|
|
|
|
if (dd->next_rq[data_dir] == rq)
|
|
dd->next_rq[data_dir] = deadline_latter_request(rq);
|
|
|
|
elv_rb_del(RQ_RB_ROOT(dd, rq), rq);
|
|
}
|
|
|
|
/*
|
|
* add rq to rbtree and fifo
|
|
*/
|
|
static void
|
|
deadline_add_request(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct deadline_data *dd = q->elevator->elevator_data;
|
|
const int data_dir = rq_data_dir(rq);
|
|
|
|
deadline_add_rq_rb(dd, rq);
|
|
|
|
/*
|
|
* set expire time (only used for reads) and add to fifo list
|
|
*/
|
|
rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
|
|
list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
|
|
}
|
|
|
|
/*
|
|
* remove rq from rbtree and fifo.
|
|
*/
|
|
static void deadline_remove_request(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct deadline_data *dd = q->elevator->elevator_data;
|
|
|
|
rq_fifo_clear(rq);
|
|
deadline_del_rq_rb(dd, rq);
|
|
}
|
|
|
|
static int
|
|
deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
|
|
{
|
|
struct deadline_data *dd = q->elevator->elevator_data;
|
|
struct request *__rq;
|
|
int ret;
|
|
|
|
/*
|
|
* check for front merge
|
|
*/
|
|
if (dd->front_merges) {
|
|
sector_t sector = bio->bi_sector + bio_sectors(bio);
|
|
|
|
__rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
|
|
if (__rq) {
|
|
BUG_ON(sector != __rq->sector);
|
|
|
|
if (elv_rq_merge_ok(__rq, bio)) {
|
|
ret = ELEVATOR_FRONT_MERGE;
|
|
goto out;
|
|
}
|
|
}
|
|
}
|
|
|
|
return ELEVATOR_NO_MERGE;
|
|
out:
|
|
*req = __rq;
|
|
return ret;
|
|
}
|
|
|
|
static void deadline_merged_request(struct request_queue *q,
|
|
struct request *req, int type)
|
|
{
|
|
struct deadline_data *dd = q->elevator->elevator_data;
|
|
|
|
/*
|
|
* if the merge was a front merge, we need to reposition request
|
|
*/
|
|
if (type == ELEVATOR_FRONT_MERGE) {
|
|
elv_rb_del(RQ_RB_ROOT(dd, req), req);
|
|
deadline_add_rq_rb(dd, req);
|
|
}
|
|
}
|
|
|
|
static void
|
|
deadline_merged_requests(struct request_queue *q, struct request *req,
|
|
struct request *next)
|
|
{
|
|
/*
|
|
* if next expires before rq, assign its expire time to rq
|
|
* and move into next position (next will be deleted) in fifo
|
|
*/
|
|
if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
|
|
if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
|
|
list_move(&req->queuelist, &next->queuelist);
|
|
rq_set_fifo_time(req, rq_fifo_time(next));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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 request *rq)
|
|
{
|
|
struct request_queue *q = rq->q;
|
|
|
|
deadline_remove_request(q, rq);
|
|
elv_dispatch_add_tail(q, rq);
|
|
}
|
|
|
|
/*
|
|
* move an entry to dispatch queue
|
|
*/
|
|
static void
|
|
deadline_move_request(struct deadline_data *dd, struct request *rq)
|
|
{
|
|
const int data_dir = rq_data_dir(rq);
|
|
|
|
dd->next_rq[READ] = NULL;
|
|
dd->next_rq[WRITE] = NULL;
|
|
dd->next_rq[data_dir] = deadline_latter_request(rq);
|
|
|
|
dd->last_sector = rq->sector + rq->nr_sectors;
|
|
|
|
/*
|
|
* take it off the sort and fifo list, move
|
|
* to dispatch queue
|
|
*/
|
|
deadline_move_to_dispatch(dd, rq);
|
|
}
|
|
|
|
/*
|
|
* 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 request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
|
|
|
|
/*
|
|
* rq is expired!
|
|
*/
|
|
if (time_after(jiffies, rq_fifo_time(rq)))
|
|
return 1;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* deadline_dispatch_requests selects the best request according to
|
|
* read/write expire, fifo_batch, etc
|
|
*/
|
|
static int deadline_dispatch_requests(struct request_queue *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 request *rq;
|
|
int data_dir;
|
|
|
|
/*
|
|
* batches are currently reads XOR writes
|
|
*/
|
|
if (dd->next_rq[WRITE])
|
|
rq = dd->next_rq[WRITE];
|
|
else
|
|
rq = dd->next_rq[READ];
|
|
|
|
if (rq) {
|
|
/* we have a "next request" */
|
|
|
|
if (dd->last_sector != rq->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_ROOT(&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_ROOT(&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) || !dd->next_rq[data_dir]) {
|
|
/*
|
|
* A deadline has expired, the last request was in the other
|
|
* direction, or we have run out of higher-sectored requests.
|
|
* Start again from the request with the earliest expiry time.
|
|
*/
|
|
rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
|
|
} else {
|
|
/*
|
|
* The last req was the same dir and we have a next request in
|
|
* sort order. No expired requests so continue on from here.
|
|
*/
|
|
rq = dd->next_rq[data_dir];
|
|
}
|
|
|
|
dd->batching = 0;
|
|
|
|
dispatch_request:
|
|
/*
|
|
* rq is the selected appropriate request.
|
|
*/
|
|
dd->batching++;
|
|
deadline_move_request(dd, rq);
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int deadline_queue_empty(struct request_queue *q)
|
|
{
|
|
struct deadline_data *dd = q->elevator->elevator_data;
|
|
|
|
return list_empty(&dd->fifo_list[WRITE])
|
|
&& list_empty(&dd->fifo_list[READ]);
|
|
}
|
|
|
|
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]));
|
|
|
|
kfree(dd);
|
|
}
|
|
|
|
/*
|
|
* initialize elevator private data (deadline_data).
|
|
*/
|
|
static void *deadline_init_queue(struct request_queue *q)
|
|
{
|
|
struct deadline_data *dd;
|
|
|
|
dd = kmalloc_node(sizeof(*dd), GFP_KERNEL | __GFP_ZERO, q->node);
|
|
if (!dd)
|
|
return NULL;
|
|
|
|
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;
|
|
}
|
|
|
|
/*
|
|
* 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 = elv_rb_former_request,
|
|
.elevator_latter_req_fn = elv_rb_latter_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)
|
|
{
|
|
return elv_register(&iosched_deadline);
|
|
}
|
|
|
|
static void __exit deadline_exit(void)
|
|
{
|
|
elv_unregister(&iosched_deadline);
|
|
}
|
|
|
|
module_init(deadline_init);
|
|
module_exit(deadline_exit);
|
|
|
|
MODULE_AUTHOR("Jens Axboe");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_DESCRIPTION("deadline IO scheduler");
|