/* * 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; } /* * the request is prepped and may have some resources allocated. * allowing unprepped requests to pass this one may cause resource * deadlock. turn on softbarrier. */ rq->flags |= REQ_SOFTBARRIER; /* * 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) { /* * the request may have been (partially) prepped. * we need to keep this request in the front to * avoid resource deadlock. turn on softbarrier. */ rq->flags |= REQ_SOFTBARRIER; 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, struct bio *bio, int 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 (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);