diff options
Diffstat (limited to 'block/elevator.c')
-rw-r--r-- | block/elevator.c | 806 |
1 files changed, 806 insertions, 0 deletions
diff --git a/block/elevator.c b/block/elevator.c new file mode 100644 index 00000000000..6c3fc8a10bf --- /dev/null +++ b/block/elevator.c @@ -0,0 +1,806 @@ +/* + * 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); + +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); + +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 void elevator_setup_default(void) +{ + struct elevator_type *e; + + /* + * If default has not been set, use the compiled-in selection. + */ + if (!chosen_elevator[0]) + strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED); + + /* + * If the given scheduler is not available, fall back to no-op. + */ + if ((e = elevator_find(chosen_elevator))) + elevator_put(e); + else + strcpy(chosen_elevator, "noop"); +} + +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; + + INIT_LIST_HEAD(&q->queue_head); + q->last_merge = NULL; + q->end_sector = 0; + q->boundary_rq = NULL; + + 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); + 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; + + /* + * 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; + } + + __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 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) +{ + if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) { + /* + * 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; + + 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; + + if (unlikely(list_empty(&q->queue_head) && + !q->elevator->ops->elevator_dispatch_fn(q, 0))) + return NULL; + + rq = list_entry_rq(q->queue_head.next); + + /* + * if this is a barrier write and the device has to issue a + * flush sequence to support it, check how far we are + */ + if (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) { + 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); + } 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); + } +} + +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)) + 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); |