/* * 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/blk.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> /* * This is a bit tricky. It's given that bio and rq are for the same * device, but the next request might of course not be. Run through * the tests below to check if we want to insert here if we can't merge * bio into an existing request */ inline int bio_rq_in_between(struct bio *bio, struct request *rq, struct list_head *head) { struct list_head *next; struct request *next_rq; /* * if .next is a valid request */ next = rq->queuelist.next; if (unlikely(next == head)) return 0; next_rq = list_entry(next, struct request, queuelist); /* * not a sector based request */ if (!(next_rq->flags & REQ_CMD)) return 0; /* * if the device is different (not a normal case) just check if * bio is after rq */ if (!kdev_same(next_rq->rq_dev, rq->rq_dev)) return bio->bi_sector > rq->sector; /* * ok, rq, next_rq and bio are on the same device. if bio is in between * the two, this is the sweet spot */ if (bio->bi_sector < next_rq->sector && bio->bi_sector > rq->sector) return 1; /* * next_rq is ordered wrt rq, but bio is not in between the two */ if (next_rq->sector > rq->sector) return 0; /* * next_rq and rq not ordered, if we happen to be either before * next_rq or after rq insert here anyway */ if (bio->bi_sector > rq->sector || bio->bi_sector < next_rq->sector) return 1; return 0; } /* * 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 (kdev_same(rq->rq_dev, to_kdev_t(bio->bi_bdev->bd_dev)) && !rq->waiting && !rq->special) return 1; return 0; } 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; } inline int elv_try_last_merge(request_queue_t *q, struct bio *bio) { int ret = ELEVATOR_NO_MERGE; /* * give a one-shot try to merging with the last touched * request */ if (q->last_merge) { struct request *__rq = list_entry_rq(q->last_merge); if (!rq_mergeable(__rq)) q->last_merge = NULL; else ret = elv_try_merge(__rq, bio); } return ret; } /* * elevator noop * * See if we can find a request that this buffer can be coalesced with. */ int elevator_noop_merge(request_queue_t *q, struct list_head **insert, struct bio *bio) { struct list_head *entry = &q->queue_head; struct request *__rq; int ret; if ((ret = elv_try_last_merge(q, bio))) { *insert = q->last_merge; return ret; } while ((entry = entry->prev) != &q->queue_head) { __rq = list_entry_rq(entry); if (__rq->flags & (REQ_BARRIER | REQ_STARTED)) break; if (!(__rq->flags & REQ_CMD)) continue; if ((ret = elv_try_merge(__rq, bio))) { *insert = &__rq->queuelist; q->last_merge = &__rq->queuelist; return ret; } } return ELEVATOR_NO_MERGE; } void elevator_noop_add_request(request_queue_t *q, struct request *rq, struct list_head *insert_here) { list_add_tail(&rq->queuelist, &q->queue_head); /* * new merges must not precede this barrier */ if (rq->flags & REQ_BARRIER) q->last_merge = NULL; else if (!q->last_merge) q->last_merge = &rq->queuelist; } struct request *elevator_noop_next_request(request_queue_t *q) { if (!list_empty(&q->queue_head)) return list_entry_rq(q->queue_head.next); return NULL; } /* * general block -> elevator interface starts here */ int elevator_init(request_queue_t *q, elevator_t *type) { elevator_t *e = &q->elevator; memcpy(e, type, sizeof(*e)); INIT_LIST_HEAD(&q->queue_head); q->last_merge = NULL; if (e->elevator_init_fn) return e->elevator_init_fn(q, e); return 0; } void elevator_exit(request_queue_t *q) { elevator_t *e = &q->elevator; if (e->elevator_exit_fn) e->elevator_exit_fn(q, e); } int elevator_global_init(void) { return 0; } int elv_merge(request_queue_t *q, struct list_head **entry, struct bio *bio) { elevator_t *e = &q->elevator; if (e->elevator_merge_fn) return e->elevator_merge_fn(q, entry, bio); return ELEVATOR_NO_MERGE; } void elv_merged_request(request_queue_t *q, struct request *rq) { elevator_t *e = &q->elevator; if (e->elevator_merged_fn) e->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 (e->elevator_merge_req_fn) e->elevator_merge_req_fn(q, rq, next); } void __elv_add_request(request_queue_t *q, struct request *rq, int at_end, int plug) { struct list_head *insert = &q->queue_head; if (at_end) insert = insert->prev; if (plug) blk_plug_device(q); q->elevator.elevator_add_req_fn(q, rq, insert); } void elv_add_request(request_queue_t *q, struct request *rq, int at_end, int plug) { unsigned long flags; spin_lock_irqsave(q->queue_lock, flags); __elv_add_request(q, rq, at_end, plug); spin_unlock_irqrestore(q->queue_lock, flags); } static inline struct request *__elv_next_request(request_queue_t *q) { return q->elevator.elevator_next_req_fn(q); } struct request *elv_next_request(request_queue_t *q) { struct request *rq; int ret; while ((rq = __elv_next_request(q))) { /* * 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->queuelist == 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) { blkdev_dequeue_request(rq); rq->flags |= REQ_QUIET; while (end_that_request_first(rq, 0, rq->nr_sectors)) ; end_that_request_last(rq); } else { printk("%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; if (e->elevator_remove_req_fn) e->elevator_remove_req_fn(q, rq); } int elv_queue_empty(request_queue_t *q) { elevator_t *e = &q->elevator; if (e->elevator_queue_empty_fn) return e->elevator_queue_empty_fn(q); return list_empty(&q->queue_head); } inline struct list_head *elv_get_sort_head(request_queue_t *q, struct request *rq) { elevator_t *e = &q->elevator; if (e->elevator_get_sort_head_fn) return e->elevator_get_sort_head_fn(q, rq); return &q->queue_head; } elevator_t elevator_noop = { elevator_merge_fn: elevator_noop_merge, elevator_next_req_fn: elevator_noop_next_request, elevator_add_req_fn: elevator_noop_add_request, }; module_init(elevator_global_init); EXPORT_SYMBOL(elevator_noop); EXPORT_SYMBOL(elv_add_request); EXPORT_SYMBOL(__elv_add_request); EXPORT_SYMBOL(elv_next_request); EXPORT_SYMBOL(elv_remove_request); EXPORT_SYMBOL(elv_queue_empty); EXPORT_SYMBOL(elevator_exit); EXPORT_SYMBOL(elevator_init);