linux/block/elevator.c
Nate Diller 248d5ca5ed [BLOCK] elevator: allow default scheduler to potentially be modular
Jens has decided that allowing the default scheduler to be a module is
a bug, and should not be allowed under kconfig.  However, I find that
scenario useful for debugging, and wish for the kernel to be able to
handle this situation without OOPSing, if I enable such an option in
the .config directly.  This patch dynamically checks for the presence
of the compiled-in default, and falls back to no-op, emitting a
suitable error message, when the default is not available

Tested for a range of boot options on 2.6.16-rc1-mm2.

Signed-off-by: Nate Diller <nate.diller@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>
2006-01-24 10:09:14 +01:00

830 lines
18 KiB
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 <linux/delay.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);
static 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;
}
static struct elevator_type *elevator_find(const char *name)
{
struct elevator_type *e = NULL;
struct list_head *entry;
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;
}
}
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;
spin_lock_irq(&elv_list_lock);
e = elevator_find(name);
if (e && !try_module_get(e->elevator_owner))
e = NULL;
spin_unlock_irq(&elv_list_lock);
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;
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 int __init elevator_setup(char *str)
{
/*
* Be backwards-compatible with previous kernels, so users
* won't get the wrong elevator.
*/
if (!strcmp(str, "as"))
strcpy(chosen_elevator, "anticipatory");
else
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;
INIT_LIST_HEAD(&q->queue_head);
q->last_merge = NULL;
q->end_sector = 0;
q->boundary_rq = NULL;
if (name && !(e = elevator_get(name)))
return -EINVAL;
if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
printk("I/O scheduler %s not found\n", chosen_elevator);
if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
printk("Default I/O scheduler not found, using no-op\n");
e = elevator_get("noop");
}
eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
if (!eq) {
elevator_put(e);
return -ENOMEM;
}
ret = elevator_attach(q, e, eq);
if (ret) {
kfree(eq);
elevator_put(e);
}
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);
}
/*
* Insert rq into dispatch queue of q. Queue lock must be held on
* entry. If sort != 0, rq is sort-inserted; otherwise, rq will be
* appended to the dispatch queue. To be used by specific elevators.
*/
void elv_dispatch_sort(request_queue_t *q, struct request *rq)
{
sector_t boundary;
struct list_head *entry;
if (q->last_merge == rq)
q->last_merge = NULL;
q->nr_sorted--;
boundary = q->end_sector;
list_for_each_prev(entry, &q->queue_head) {
struct request *pos = list_entry_rq(entry);
if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
break;
if (rq->sector >= boundary) {
if (pos->sector < boundary)
continue;
} else {
if (pos->sector >= boundary)
break;
}
if (rq->sector >= pos->sector)
break;
}
list_add(&rq->queuelist, entry);
}
int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
elevator_t *e = q->elevator;
int ret;
if (q->last_merge) {
ret = elv_try_merge(q->last_merge, bio);
if (ret != ELEVATOR_NO_MERGE) {
*req = q->last_merge;
return ret;
}
}
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);
q->last_merge = rq;
}
void elv_merge_requests(request_queue_t *q, struct request *rq,
struct request *next)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_merge_req_fn)
e->ops->elevator_merge_req_fn(q, rq, next);
q->nr_sorted--;
q->last_merge = rq;
}
void elv_requeue_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--;
if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
e->ops->elevator_deactivate_req_fn(q, rq);
}
rq->flags &= ~REQ_STARTED;
__elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE, 0);
}
static void elv_drain_elevator(request_queue_t *q)
{
static int printed;
while (q->elevator->ops->elevator_dispatch_fn(q, 1))
;
if (q->nr_sorted == 0)
return;
if (printed++ < 10) {
printk(KERN_ERR "%s: forced dispatching is broken "
"(nr_sorted=%u), please report this\n",
q->elevator->elevator_type->elevator_name, q->nr_sorted);
}
}
void __elv_add_request(request_queue_t *q, struct request *rq, int where,
int plug)
{
struct list_head *pos;
unsigned ordseq;
if (q->ordcolor)
rq->flags |= REQ_ORDERED_COLOR;
if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
/*
* toggle ordered color
*/
q->ordcolor ^= 1;
/*
* barriers implicitly indicate back insertion
*/
if (where == ELEVATOR_INSERT_SORT)
where = ELEVATOR_INSERT_BACK;
/*
* this request is scheduling boundary, update end_sector
*/
if (blk_fs_request(rq)) {
q->end_sector = rq_end_sector(rq);
q->boundary_rq = rq;
}
} else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
where = ELEVATOR_INSERT_BACK;
if (plug)
blk_plug_device(q);
rq->q = q;
switch (where) {
case ELEVATOR_INSERT_FRONT:
rq->flags |= REQ_SOFTBARRIER;
list_add(&rq->queuelist, &q->queue_head);
break;
case ELEVATOR_INSERT_BACK:
rq->flags |= REQ_SOFTBARRIER;
elv_drain_elevator(q);
list_add_tail(&rq->queuelist, &q->queue_head);
/*
* We kick the queue here for the following reasons.
* - The elevator might have returned NULL previously
* to delay requests and returned them now. As the
* queue wasn't empty before this request, ll_rw_blk
* won't run the queue on return, resulting in hang.
* - Usually, back inserted requests won't be merged
* with anything. There's no point in delaying queue
* processing.
*/
blk_remove_plug(q);
q->request_fn(q);
break;
case ELEVATOR_INSERT_SORT:
BUG_ON(!blk_fs_request(rq));
rq->flags |= REQ_SORTED;
q->nr_sorted++;
if (q->last_merge == NULL && rq_mergeable(rq))
q->last_merge = rq;
/*
* Some ioscheds (cfq) run q->request_fn directly, so
* rq cannot be accessed after calling
* elevator_add_req_fn.
*/
q->elevator->ops->elevator_add_req_fn(q, rq);
break;
case ELEVATOR_INSERT_REQUEUE:
/*
* If ordered flush isn't in progress, we do front
* insertion; otherwise, requests should be requeued
* in ordseq order.
*/
rq->flags |= REQ_SOFTBARRIER;
if (q->ordseq == 0) {
list_add(&rq->queuelist, &q->queue_head);
break;
}
ordseq = blk_ordered_req_seq(rq);
list_for_each(pos, &q->queue_head) {
struct request *pos_rq = list_entry_rq(pos);
if (ordseq <= blk_ordered_req_seq(pos_rq))
break;
}
list_add_tail(&rq->queuelist, pos);
break;
default:
printk(KERN_ERR "%s: bad insertion point %d\n",
__FUNCTION__, where);
BUG();
}
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);
}
}
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;
while (1) {
while (!list_empty(&q->queue_head)) {
rq = list_entry_rq(q->queue_head.next);
if (blk_do_ordered(q, &rq))
return rq;
}
if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
return NULL;
}
}
struct request *elv_next_request(request_queue_t *q)
{
struct request *rq;
int ret;
while ((rq = __elv_next_request(q)) != NULL) {
if (!(rq->flags & REQ_STARTED)) {
elevator_t *e = q->elevator;
/*
* This is the first time the device driver
* sees this request (possibly after
* requeueing). Notify IO scheduler.
*/
if (blk_sorted_rq(rq) &&
e->ops->elevator_activate_req_fn)
e->ops->elevator_activate_req_fn(q, rq);
/*
* 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 (!q->boundary_rq || q->boundary_rq == rq) {
q->end_sector = rq_end_sector(rq);
q->boundary_rq = 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) {
/*
* the request may have been (partially) prepped.
* we need to keep this request in the front to
* avoid resource deadlock. REQ_STARTED will
* prevent other fs requests from passing this one.
*/
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, 0);
} else {
printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
ret);
break;
}
}
return rq;
}
void elv_dequeue_request(request_queue_t *q, struct request *rq)
{
BUG_ON(list_empty(&rq->queuelist));
list_del_init(&rq->queuelist);
/*
* 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.
*/
if (blk_account_rq(rq))
q->in_flight++;
}
int elv_queue_empty(request_queue_t *q)
{
elevator_t *e = q->elevator;
if (!list_empty(&q->queue_head))
return 0;
if (e->ops->elevator_queue_empty_fn)
return e->ops->elevator_queue_empty_fn(q);
return 1;
}
struct request *elv_latter_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_latter_req_fn)
return e->ops->elevator_latter_req_fn(q, rq);
return NULL;
}
struct request *elv_former_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_former_req_fn)
return e->ops->elevator_former_req_fn(q, rq);
return NULL;
}
int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
gfp_t gfp_mask)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_set_req_fn)
return e->ops->elevator_set_req_fn(q, rq, bio, 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, struct bio *bio)
{
elevator_t *e = q->elevator;
if (e->ops->elevator_may_queue_fn)
return e->ops->elevator_may_queue_fn(q, rw, bio);
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 (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
e->ops->elevator_completed_req_fn(q, rq);
}
/*
* Check if the queue is waiting for fs requests to be
* drained for flush sequence.
*/
if (unlikely(q->ordseq)) {
struct request *first_rq = list_entry_rq(q->queue_head.next);
if (q->in_flight == 0 &&
blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
q->request_fn(q);
}
}
}
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)
{
spin_lock_irq(&elv_list_lock);
if (elevator_find(e->elevator_name))
BUG();
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) ||
(!*chosen_elevator &&
!strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
printk(" (default)");
printk("\n");
return 0;
}
EXPORT_SYMBOL_GPL(elv_register);
void elv_unregister(struct elevator_type *e)
{
struct task_struct *g, *p;
/*
* Iterate every thread in the process to remove the io contexts.
*/
read_lock(&tasklist_lock);
do_each_thread(g, p) {
struct io_context *ioc = p->io_context;
if (ioc && ioc->cic) {
ioc->cic->exit(ioc->cic);
ioc->cic->dtor(ioc->cic);
ioc->cic = NULL;
}
if (ioc && ioc->aic) {
ioc->aic->exit(ioc->aic);
ioc->aic->dtor(ioc->aic);
ioc->aic = NULL;
}
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
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.
*/
static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
{
elevator_t *old_elevator, *e;
/*
* Allocate new elevator
*/
e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
if (!e)
goto error;
/*
* Turn on BYPASS and drain all requests w/ elevator private data
*/
spin_lock_irq(q->queue_lock);
set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
elv_drain_elevator(q);
while (q->rq.elvpriv) {
blk_remove_plug(q);
q->request_fn(q);
spin_unlock_irq(q->queue_lock);
msleep(10);
spin_lock_irq(q->queue_lock);
elv_drain_elevator(q);
}
spin_unlock_irq(q->queue_lock);
/*
* unregister old elevator data
*/
elv_unregister_queue(q);
old_elevator = q->elevator;
/*
* 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 turn off BYPASS.
*/
elevator_exit(old_elevator);
clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
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);
e = NULL;
fail:
q->elevator = old_elevator;
elv_register_queue(q);
clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
kfree(e);
error:
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];
size_t len;
struct elevator_type *e;
elevator_name[sizeof(elevator_name) - 1] = '\0';
strncpy(elevator_name, name, sizeof(elevator_name) - 1);
len = strlen(elevator_name);
if (len && elevator_name[len - 1] == '\n')
elevator_name[len - 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)) {
elevator_put(e);
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_dispatch_sort);
EXPORT_SYMBOL(elv_add_request);
EXPORT_SYMBOL(__elv_add_request);
EXPORT_SYMBOL(elv_requeue_request);
EXPORT_SYMBOL(elv_next_request);
EXPORT_SYMBOL(elv_dequeue_request);
EXPORT_SYMBOL(elv_queue_empty);
EXPORT_SYMBOL(elv_completed_request);
EXPORT_SYMBOL(elevator_exit);
EXPORT_SYMBOL(elevator_init);