linux/drivers/block/elevator.c

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/*
* linux/drivers/block/elevator.c
*
* Block device elevator/IO-scheduler.
*
* Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
*
* 30042000 Jens Axboe <axboe@suse.de> :
*
* Split the elevator a bit so that it is possible to choose a different
* one or even write a new "plug in". There are three pieces:
* - elevator_fn, inserts a new request in the queue list
* - elevator_merge_fn, decides whether a new buffer can be merged with
* an existing request
* - elevator_dequeue_fn, called when a request is taken off the active list
*
* 20082000 Dave Jones <davej@suse.de> :
* Removed tests for max-bomb-segments, which was breaking elvtune
* when run without -bN
*
* Jens:
* - Rework again to work with bio instead of buffer_heads
* - loose bi_dev comparisons, partition handling is right now
* - completely modularize elevator setup and teardown
*
*/
#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 <asm/uaccess.h>
static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);
/*
* can we safely merge with this request?
*/
inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
{
if (!rq_mergeable(rq))
return 0;
/*
* different data direction or already started, don't merge
*/
if (bio_data_dir(bio) != rq_data_dir(rq))
return 0;
/*
* same device and no special stuff set, merge is ok
*/
if (rq->rq_disk == bio->bi_bdev->bd_disk &&
!rq->waiting && !rq->special)
return 1;
return 0;
}
EXPORT_SYMBOL(elv_rq_merge_ok);
inline int elv_try_merge(struct request *__rq, struct bio *bio)
{
int ret = ELEVATOR_NO_MERGE;
/*
* we can merge and sequence is ok, check if it's possible
*/
if (elv_rq_merge_ok(__rq, bio)) {
if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
ret = ELEVATOR_BACK_MERGE;
else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
ret = ELEVATOR_FRONT_MERGE;
}
return ret;
}
EXPORT_SYMBOL(elv_try_merge);
inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
{
if (q->last_merge)
return elv_try_merge(q->last_merge, bio);
return ELEVATOR_NO_MERGE;
}
EXPORT_SYMBOL(elv_try_last_merge);
static struct elevator_type *elevator_find(const char *name)
{
struct elevator_type *e = NULL;
struct list_head *entry;
spin_lock_irq(&elv_list_lock);
list_for_each(entry, &elv_list) {
struct elevator_type *__e;
__e = list_entry(entry, struct elevator_type, list);
if (!strcmp(__e->elevator_name, name)) {
e = __e;
break;
}
}
spin_unlock_irq(&elv_list_lock);
return e;
}
static void elevator_put(struct elevator_type *e)
{
module_put(e->elevator_owner);
}
static struct elevator_type *elevator_get(const char *name)
{
struct elevator_type *e = elevator_find(name);
if (!e)
return NULL;
if (!try_module_get(e->elevator_owner))
return NULL;
return e;
}
static int elevator_attach(request_queue_t *q, struct elevator_type *e,
struct elevator_queue *eq)
{
int ret = 0;
memset(eq, 0, sizeof(*eq));
eq->ops = &e->ops;
eq->elevator_type = e;
INIT_LIST_HEAD(&q->queue_head);
q->last_merge = NULL;
q->elevator = eq;
if (eq->ops->elevator_init_fn)
ret = eq->ops->elevator_init_fn(q, eq);
return ret;
}
static char chosen_elevator[16];
static void elevator_setup_default(void)
{
/*
* check if default is set and exists
*/
if (chosen_elevator[0] && elevator_find(chosen_elevator))
return;
#if defined(CONFIG_IOSCHED_AS)
strcpy(chosen_elevator, "anticipatory");
#elif defined(CONFIG_IOSCHED_DEADLINE)
strcpy(chosen_elevator, "deadline");
#elif defined(CONFIG_IOSCHED_CFQ)
strcpy(chosen_elevator, "cfq");
#elif defined(CONFIG_IOSCHED_NOOP)
strcpy(chosen_elevator, "noop");
#else
#error "You must build at least 1 IO scheduler into the kernel"
#endif
}
static int __init elevator_setup(char *str)
{
strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
return 0;
}
__setup("elevator=", elevator_setup);
int elevator_init(request_queue_t *q, char *name)
{
struct elevator_type *e = NULL;
struct elevator_queue *eq;
int ret = 0;
elevator_setup_default();
if (!name)
name = chosen_elevator;
e = elevator_get(name);
if (!e)
return -EINVAL;
eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
if (!eq) {
elevator_put(e->elevator_type);
return -ENOMEM;
}
ret = elevator_attach(q, e, eq);
if (ret) {
kfree(eq);
elevator_put(e->elevator_type);
}
return ret;
}
void elevator_exit(elevator_t *e)
{
if (e->ops->elevator_exit_fn)
e->ops->elevator_exit_fn(e);
elevator_put(e->elevator_type);
e->elevator_type = NULL;
kfree(e);
}
int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_merge_fn)
return e->ops->elevator_merge_fn(q, req, bio);
return ELEVATOR_NO_MERGE;
}
void elv_merged_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_merged_fn)
e->ops->elevator_merged_fn(q, rq);
}
void elv_merge_requests(request_queue_t *q, struct request *rq,
struct request *next)
{
elevator_t *e = q->elevator;
if (q->last_merge == next)
q->last_merge = NULL;
if (e->ops->elevator_merge_req_fn)
e->ops->elevator_merge_req_fn(q, rq, next);
}
/*
* For careful internal use by the block layer. Essentially the same as
* a requeue in that it tells the io scheduler that this request is not
* active in the driver or hardware anymore, but we don't want the request
* added back to the scheduler. Function is not exported.
*/
void elv_deactivate_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
/*
* it already went through dequeue, we need to decrement the
* in_flight count again
*/
if (blk_account_rq(rq))
q->in_flight--;
rq->flags &= ~REQ_STARTED;
if (e->ops->elevator_deactivate_req_fn)
e->ops->elevator_deactivate_req_fn(q, rq);
}
void elv_requeue_request(request_queue_t *q, struct request *rq)
{
elv_deactivate_request(q, rq);
/*
* if this is the flush, requeue the original instead and drop the flush
*/
if (rq->flags & REQ_BAR_FLUSH) {
clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
rq = rq->end_io_data;
}
/*
* if iosched has an explicit requeue hook, then use that. otherwise
* just put the request at the front of the queue
*/
if (q->elevator->ops->elevator_requeue_req_fn)
q->elevator->ops->elevator_requeue_req_fn(q, rq);
else
__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
}
void __elv_add_request(request_queue_t *q, struct request *rq, int where,
int plug)
{
/*
* barriers implicitly indicate back insertion
*/
if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&
where == ELEVATOR_INSERT_SORT)
where = ELEVATOR_INSERT_BACK;
if (plug)
blk_plug_device(q);
rq->q = q;
if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {
q->elevator->ops->elevator_add_req_fn(q, rq, where);
if (blk_queue_plugged(q)) {
int nrq = q->rq.count[READ] + q->rq.count[WRITE]
- q->in_flight;
if (nrq >= q->unplug_thresh)
__generic_unplug_device(q);
}
} else
/*
* if drain is set, store the request "locally". when the drain
* is finished, the requests will be handed ordered to the io
* scheduler
*/
list_add_tail(&rq->queuelist, &q->drain_list);
}
void elv_add_request(request_queue_t *q, struct request *rq, int where,
int plug)
{
unsigned long flags;
spin_lock_irqsave(q->queue_lock, flags);
__elv_add_request(q, rq, where, plug);
spin_unlock_irqrestore(q->queue_lock, flags);
}
static inline struct request *__elv_next_request(request_queue_t *q)
{
struct request *rq = q->elevator->ops->elevator_next_req_fn(q);
/*
* if this is a barrier write and the device has to issue a
* flush sequence to support it, check how far we are
*/
if (rq && blk_fs_request(rq) && blk_barrier_rq(rq)) {
BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
if (q->ordered == QUEUE_ORDERED_FLUSH &&
!blk_barrier_preflush(rq))
rq = blk_start_pre_flush(q, rq);
}
return rq;
}
struct request *elv_next_request(request_queue_t *q)
{
struct request *rq;
int ret;
while ((rq = __elv_next_request(q)) != NULL) {
/*
* just mark as started even if we don't start it, a request
* that has been delayed should not be passed by new incoming
* requests
*/
rq->flags |= REQ_STARTED;
if (rq == q->last_merge)
q->last_merge = NULL;
if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
break;
ret = q->prep_rq_fn(q, rq);
if (ret == BLKPREP_OK) {
break;
} else if (ret == BLKPREP_DEFER) {
rq = NULL;
break;
} else if (ret == BLKPREP_KILL) {
int nr_bytes = rq->hard_nr_sectors << 9;
if (!nr_bytes)
nr_bytes = rq->data_len;
blkdev_dequeue_request(rq);
rq->flags |= REQ_QUIET;
end_that_request_chunk(rq, 0, nr_bytes);
end_that_request_last(rq);
} else {
printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
ret);
break;
}
}
return rq;
}
void elv_remove_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
/*
* the time frame between a request being removed from the lists
* and to it is freed is accounted as io that is in progress at
* the driver side. note that we only account requests that the
* driver has seen (REQ_STARTED set), to avoid false accounting
* for request-request merges
*/
if (blk_account_rq(rq))
q->in_flight++;
/*
* the main clearing point for q->last_merge is on retrieval of
* request by driver (it calls elv_next_request()), but it _can_
* also happen here if a request is added to the queue but later
* deleted without ever being given to driver (merged with another
* request).
*/
if (rq == q->last_merge)
q->last_merge = NULL;
if (e->ops->elevator_remove_req_fn)
e->ops->elevator_remove_req_fn(q, rq);
}
int elv_queue_empty(request_queue_t *q)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_queue_empty_fn)
return e->ops->elevator_queue_empty_fn(q);
return list_empty(&q->queue_head);
}
struct request *elv_latter_request(request_queue_t *q, struct request *rq)
{
struct list_head *next;
elevator_t *e = q->elevator;
if (e->ops->elevator_latter_req_fn)
return e->ops->elevator_latter_req_fn(q, rq);
next = rq->queuelist.next;
if (next != &q->queue_head && next != &rq->queuelist)
return list_entry_rq(next);
return NULL;
}
struct request *elv_former_request(request_queue_t *q, struct request *rq)
{
struct list_head *prev;
elevator_t *e = q->elevator;
if (e->ops->elevator_former_req_fn)
return e->ops->elevator_former_req_fn(q, rq);
prev = rq->queuelist.prev;
if (prev != &q->queue_head && prev != &rq->queuelist)
return list_entry_rq(prev);
return NULL;
}
int elv_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_set_req_fn)
return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
rq->elevator_private = NULL;
return 0;
}
void elv_put_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_put_req_fn)
e->ops->elevator_put_req_fn(q, rq);
}
int elv_may_queue(request_queue_t *q, int rw)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_may_queue_fn)
return e->ops->elevator_may_queue_fn(q, rw);
return ELV_MQUEUE_MAY;
}
void elv_completed_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
/*
* request is released from the driver, io must be done
*/
if (blk_account_rq(rq))
q->in_flight--;
if (e->ops->elevator_completed_req_fn)
e->ops->elevator_completed_req_fn(q, rq);
}
int elv_register_queue(struct request_queue *q)
{
elevator_t *e = q->elevator;
e->kobj.parent = kobject_get(&q->kobj);
if (!e->kobj.parent)
return -EBUSY;
snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
e->kobj.ktype = e->elevator_type->elevator_ktype;
return kobject_register(&e->kobj);
}
void elv_unregister_queue(struct request_queue *q)
{
if (q) {
elevator_t *e = q->elevator;
kobject_unregister(&e->kobj);
kobject_put(&q->kobj);
}
}
int elv_register(struct elevator_type *e)
{
if (elevator_find(e->elevator_name))
BUG();
spin_lock_irq(&elv_list_lock);
list_add_tail(&e->list, &elv_list);
spin_unlock_irq(&elv_list_lock);
printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
if (!strcmp(e->elevator_name, chosen_elevator))
printk(" (default)");
printk("\n");
return 0;
}
EXPORT_SYMBOL_GPL(elv_register);
void elv_unregister(struct elevator_type *e)
{
spin_lock_irq(&elv_list_lock);
list_del_init(&e->list);
spin_unlock_irq(&elv_list_lock);
}
EXPORT_SYMBOL_GPL(elv_unregister);
/*
* switch to new_e io scheduler. be careful not to introduce deadlocks -
* we don't free the old io scheduler, before we have allocated what we
* need for the new one. this way we have a chance of going back to the old
* one, if the new one fails init for some reason. we also do an intermediate
* switch to noop to ensure safety with stack-allocated requests, since they
* don't originate from the block layer allocator. noop is safe here, because
* it never needs to touch the elevator itself for completion events. DRAIN
* flags will make sure we don't touch it for additions either.
*/
static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
{
elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
struct elevator_type *noop_elevator = NULL;
elevator_t *old_elevator;
if (!e)
goto error;
/*
* first step, drain requests from the block freelist
*/
blk_wait_queue_drained(q, 0);
/*
* unregister old elevator data
*/
elv_unregister_queue(q);
old_elevator = q->elevator;
/*
* next step, switch to noop since it uses no private rq structures
* and doesn't allocate any memory for anything. then wait for any
* non-fs requests in-flight
*/
noop_elevator = elevator_get("noop");
spin_lock_irq(q->queue_lock);
elevator_attach(q, noop_elevator, e);
spin_unlock_irq(q->queue_lock);
blk_wait_queue_drained(q, 1);
/*
* attach and start new elevator
*/
if (elevator_attach(q, new_e, e))
goto fail;
if (elv_register_queue(q))
goto fail_register;
/*
* finally exit old elevator and start queue again
*/
elevator_exit(old_elevator);
blk_finish_queue_drain(q);
elevator_put(noop_elevator);
return;
fail_register:
/*
* switch failed, exit the new io scheduler and reattach the old
* one again (along with re-adding the sysfs dir)
*/
elevator_exit(e);
fail:
q->elevator = old_elevator;
elv_register_queue(q);
blk_finish_queue_drain(q);
error:
if (noop_elevator)
elevator_put(noop_elevator);
elevator_put(new_e);
printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
}
ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
{
char elevator_name[ELV_NAME_MAX];
struct elevator_type *e;
memset(elevator_name, 0, sizeof(elevator_name));
strncpy(elevator_name, name, sizeof(elevator_name));
if (elevator_name[strlen(elevator_name) - 1] == '\n')
elevator_name[strlen(elevator_name) - 1] = '\0';
e = elevator_get(elevator_name);
if (!e) {
printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
return -EINVAL;
}
if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
return count;
elevator_switch(q, e);
return count;
}
ssize_t elv_iosched_show(request_queue_t *q, char *name)
{
elevator_t *e = q->elevator;
struct elevator_type *elv = e->elevator_type;
struct list_head *entry;
int len = 0;
spin_lock_irq(q->queue_lock);
list_for_each(entry, &elv_list) {
struct elevator_type *__e;
__e = list_entry(entry, struct elevator_type, list);
if (!strcmp(elv->elevator_name, __e->elevator_name))
len += sprintf(name+len, "[%s] ", elv->elevator_name);
else
len += sprintf(name+len, "%s ", __e->elevator_name);
}
spin_unlock_irq(q->queue_lock);
len += sprintf(len+name, "\n");
return len;
}
EXPORT_SYMBOL(elv_add_request);
EXPORT_SYMBOL(__elv_add_request);
EXPORT_SYMBOL(elv_requeue_request);
EXPORT_SYMBOL(elv_next_request);
EXPORT_SYMBOL(elv_remove_request);
EXPORT_SYMBOL(elv_queue_empty);
EXPORT_SYMBOL(elv_completed_request);
EXPORT_SYMBOL(elevator_exit);
EXPORT_SYMBOL(elevator_init);