// SPDX-License-Identifier: GPL-2.0 /* * Block device elevator/IO-scheduler. * * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE * * 30042000 Jens Axboe <axboe@kernel.dk> : * * 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/bio.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/compiler.h> #include <linux/blktrace_api.h> #include <linux/hash.h> #include <linux/uaccess.h> #include <linux/pm_runtime.h> #include <linux/blk-cgroup.h> #include <trace/events/block.h> #include "elevator.h" #include "blk.h" #include "blk-mq-sched.h" #include "blk-pm.h" #include "blk-wbt.h" static DEFINE_SPINLOCK(elv_list_lock); static LIST_HEAD(elv_list); /* * Merge hash stuff. */ #define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq)) /* * Query io scheduler to see if the current process issuing bio may be * merged with rq. */ static int elv_iosched_allow_bio_merge(struct request *rq, struct bio *bio) { struct request_queue *q = rq->q; struct elevator_queue *e = q->elevator; if (e->type->ops.allow_merge) return e->type->ops.allow_merge(q, rq, bio); return 1; } /* * can we safely merge with this request? */ bool elv_bio_merge_ok(struct request *rq, struct bio *bio) { if (!blk_rq_merge_ok(rq, bio)) return false; if (!elv_iosched_allow_bio_merge(rq, bio)) return false; return true; } EXPORT_SYMBOL(elv_bio_merge_ok); static inline bool elv_support_features(unsigned int elv_features, unsigned int required_features) { return (required_features & elv_features) == required_features; } /** * elevator_match - Test an elevator name and features * @e: Scheduler to test * @name: Elevator name to test * @required_features: Features that the elevator must provide * * Return true if the elevator @e name matches @name and if @e provides all * the features specified by @required_features. */ static bool elevator_match(const struct elevator_type *e, const char *name, unsigned int required_features) { if (!elv_support_features(e->elevator_features, required_features)) return false; if (!strcmp(e->elevator_name, name)) return true; if (e->elevator_alias && !strcmp(e->elevator_alias, name)) return true; return false; } /** * elevator_find - Find an elevator * @name: Name of the elevator to find * @required_features: Features that the elevator must provide * * Return the first registered scheduler with name @name and supporting the * features @required_features and NULL otherwise. */ static struct elevator_type *elevator_find(const char *name, unsigned int required_features) { struct elevator_type *e; list_for_each_entry(e, &elv_list, list) { if (elevator_match(e, name, required_features)) return e; } return NULL; } static void elevator_put(struct elevator_type *e) { module_put(e->elevator_owner); } static struct elevator_type *elevator_get(struct request_queue *q, const char *name, bool try_loading) { struct elevator_type *e; spin_lock(&elv_list_lock); e = elevator_find(name, q->required_elevator_features); if (!e && try_loading) { spin_unlock(&elv_list_lock); request_module("%s-iosched", name); spin_lock(&elv_list_lock); e = elevator_find(name, q->required_elevator_features); } if (e && !try_module_get(e->elevator_owner)) e = NULL; spin_unlock(&elv_list_lock); return e; } static struct kobj_type elv_ktype; struct elevator_queue *elevator_alloc(struct request_queue *q, struct elevator_type *e) { struct elevator_queue *eq; eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node); if (unlikely(!eq)) return NULL; eq->type = e; kobject_init(&eq->kobj, &elv_ktype); mutex_init(&eq->sysfs_lock); hash_init(eq->hash); return eq; } EXPORT_SYMBOL(elevator_alloc); static void elevator_release(struct kobject *kobj) { struct elevator_queue *e; e = container_of(kobj, struct elevator_queue, kobj); elevator_put(e->type); kfree(e); } void __elevator_exit(struct request_queue *q, struct elevator_queue *e) { mutex_lock(&e->sysfs_lock); blk_mq_exit_sched(q, e); mutex_unlock(&e->sysfs_lock); kobject_put(&e->kobj); } static inline void __elv_rqhash_del(struct request *rq) { hash_del(&rq->hash); rq->rq_flags &= ~RQF_HASHED; } void elv_rqhash_del(struct request_queue *q, struct request *rq) { if (ELV_ON_HASH(rq)) __elv_rqhash_del(rq); } EXPORT_SYMBOL_GPL(elv_rqhash_del); void elv_rqhash_add(struct request_queue *q, struct request *rq) { struct elevator_queue *e = q->elevator; BUG_ON(ELV_ON_HASH(rq)); hash_add(e->hash, &rq->hash, rq_hash_key(rq)); rq->rq_flags |= RQF_HASHED; } EXPORT_SYMBOL_GPL(elv_rqhash_add); void elv_rqhash_reposition(struct request_queue *q, struct request *rq) { __elv_rqhash_del(rq); elv_rqhash_add(q, rq); } struct request *elv_rqhash_find(struct request_queue *q, sector_t offset) { struct elevator_queue *e = q->elevator; struct hlist_node *next; struct request *rq; hash_for_each_possible_safe(e->hash, rq, next, hash, offset) { BUG_ON(!ELV_ON_HASH(rq)); if (unlikely(!rq_mergeable(rq))) { __elv_rqhash_del(rq); continue; } if (rq_hash_key(rq) == offset) return rq; } return NULL; } /* * RB-tree support functions for inserting/lookup/removal of requests * in a sorted RB tree. */ void elv_rb_add(struct rb_root *root, struct request *rq) { struct rb_node **p = &root->rb_node; struct rb_node *parent = NULL; struct request *__rq; while (*p) { parent = *p; __rq = rb_entry(parent, struct request, rb_node); if (blk_rq_pos(rq) < blk_rq_pos(__rq)) p = &(*p)->rb_left; else if (blk_rq_pos(rq) >= blk_rq_pos(__rq)) p = &(*p)->rb_right; } rb_link_node(&rq->rb_node, parent, p); rb_insert_color(&rq->rb_node, root); } EXPORT_SYMBOL(elv_rb_add); void elv_rb_del(struct rb_root *root, struct request *rq) { BUG_ON(RB_EMPTY_NODE(&rq->rb_node)); rb_erase(&rq->rb_node, root); RB_CLEAR_NODE(&rq->rb_node); } EXPORT_SYMBOL(elv_rb_del); struct request *elv_rb_find(struct rb_root *root, sector_t sector) { struct rb_node *n = root->rb_node; struct request *rq; while (n) { rq = rb_entry(n, struct request, rb_node); if (sector < blk_rq_pos(rq)) n = n->rb_left; else if (sector > blk_rq_pos(rq)) n = n->rb_right; else return rq; } return NULL; } EXPORT_SYMBOL(elv_rb_find); enum elv_merge elv_merge(struct request_queue *q, struct request **req, struct bio *bio) { struct elevator_queue *e = q->elevator; struct request *__rq; /* * Levels of merges: * nomerges: No merges at all attempted * noxmerges: Only simple one-hit cache try * merges: All merge tries attempted */ if (blk_queue_nomerges(q) || !bio_mergeable(bio)) return ELEVATOR_NO_MERGE; /* * First try one-hit cache. */ if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) { enum elv_merge ret = blk_try_merge(q->last_merge, bio); if (ret != ELEVATOR_NO_MERGE) { *req = q->last_merge; return ret; } } if (blk_queue_noxmerges(q)) return ELEVATOR_NO_MERGE; /* * See if our hash lookup can find a potential backmerge. */ __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector); if (__rq && elv_bio_merge_ok(__rq, bio)) { *req = __rq; if (blk_discard_mergable(__rq)) return ELEVATOR_DISCARD_MERGE; return ELEVATOR_BACK_MERGE; } if (e->type->ops.request_merge) return e->type->ops.request_merge(q, req, bio); return ELEVATOR_NO_MERGE; } /* * Attempt to do an insertion back merge. Only check for the case where * we can append 'rq' to an existing request, so we can throw 'rq' away * afterwards. * * Returns true if we merged, false otherwise. 'free' will contain all * requests that need to be freed. */ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq, struct list_head *free) { struct request *__rq; bool ret; if (blk_queue_nomerges(q)) return false; /* * First try one-hit cache. */ if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq)) { list_add(&rq->queuelist, free); return true; } if (blk_queue_noxmerges(q)) return false; ret = false; /* * See if our hash lookup can find a potential backmerge. */ while (1) { __rq = elv_rqhash_find(q, blk_rq_pos(rq)); if (!__rq || !blk_attempt_req_merge(q, __rq, rq)) break; list_add(&rq->queuelist, free); /* The merged request could be merged with others, try again */ ret = true; rq = __rq; } return ret; } void elv_merged_request(struct request_queue *q, struct request *rq, enum elv_merge type) { struct elevator_queue *e = q->elevator; if (e->type->ops.request_merged) e->type->ops.request_merged(q, rq, type); if (type == ELEVATOR_BACK_MERGE) elv_rqhash_reposition(q, rq); q->last_merge = rq; } void elv_merge_requests(struct request_queue *q, struct request *rq, struct request *next) { struct elevator_queue *e = q->elevator; if (e->type->ops.requests_merged) e->type->ops.requests_merged(q, rq, next); elv_rqhash_reposition(q, rq); q->last_merge = rq; } struct request *elv_latter_request(struct request_queue *q, struct request *rq) { struct elevator_queue *e = q->elevator; if (e->type->ops.next_request) return e->type->ops.next_request(q, rq); return NULL; } struct request *elv_former_request(struct request_queue *q, struct request *rq) { struct elevator_queue *e = q->elevator; if (e->type->ops.former_request) return e->type->ops.former_request(q, rq); return NULL; } #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr) static ssize_t elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page) { struct elv_fs_entry *entry = to_elv(attr); struct elevator_queue *e; ssize_t error; if (!entry->show) return -EIO; e = container_of(kobj, struct elevator_queue, kobj); mutex_lock(&e->sysfs_lock); error = e->type ? entry->show(e, page) : -ENOENT; mutex_unlock(&e->sysfs_lock); return error; } static ssize_t elv_attr_store(struct kobject *kobj, struct attribute *attr, const char *page, size_t length) { struct elv_fs_entry *entry = to_elv(attr); struct elevator_queue *e; ssize_t error; if (!entry->store) return -EIO; e = container_of(kobj, struct elevator_queue, kobj); mutex_lock(&e->sysfs_lock); error = e->type ? entry->store(e, page, length) : -ENOENT; mutex_unlock(&e->sysfs_lock); return error; } static const struct sysfs_ops elv_sysfs_ops = { .show = elv_attr_show, .store = elv_attr_store, }; static struct kobj_type elv_ktype = { .sysfs_ops = &elv_sysfs_ops, .release = elevator_release, }; int elv_register_queue(struct request_queue *q, bool uevent) { struct elevator_queue *e = q->elevator; int error; lockdep_assert_held(&q->sysfs_lock); error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched"); if (!error) { struct elv_fs_entry *attr = e->type->elevator_attrs; if (attr) { while (attr->attr.name) { if (sysfs_create_file(&e->kobj, &attr->attr)) break; attr++; } } if (uevent) kobject_uevent(&e->kobj, KOBJ_ADD); e->registered = 1; } return error; } void elv_unregister_queue(struct request_queue *q) { lockdep_assert_held(&q->sysfs_lock); if (q) { struct elevator_queue *e = q->elevator; kobject_uevent(&e->kobj, KOBJ_REMOVE); kobject_del(&e->kobj); e->registered = 0; /* Re-enable throttling in case elevator disabled it */ wbt_enable_default(q); } } int elv_register(struct elevator_type *e) { /* insert_requests and dispatch_request are mandatory */ if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request)) return -EINVAL; /* create icq_cache if requested */ if (e->icq_size) { if (WARN_ON(e->icq_size < sizeof(struct io_cq)) || WARN_ON(e->icq_align < __alignof__(struct io_cq))) return -EINVAL; snprintf(e->icq_cache_name, sizeof(e->icq_cache_name), "%s_io_cq", e->elevator_name); e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size, e->icq_align, 0, NULL); if (!e->icq_cache) return -ENOMEM; } /* register, don't allow duplicate names */ spin_lock(&elv_list_lock); if (elevator_find(e->elevator_name, 0)) { spin_unlock(&elv_list_lock); kmem_cache_destroy(e->icq_cache); return -EBUSY; } list_add_tail(&e->list, &elv_list); spin_unlock(&elv_list_lock); printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name); return 0; } EXPORT_SYMBOL_GPL(elv_register); void elv_unregister(struct elevator_type *e) { /* unregister */ spin_lock(&elv_list_lock); list_del_init(&e->list); spin_unlock(&elv_list_lock); /* * Destroy icq_cache if it exists. icq's are RCU managed. Make * sure all RCU operations are complete before proceeding. */ if (e->icq_cache) { rcu_barrier(); kmem_cache_destroy(e->icq_cache); e->icq_cache = NULL; } } EXPORT_SYMBOL_GPL(elv_unregister); int elevator_switch_mq(struct request_queue *q, struct elevator_type *new_e) { int ret; lockdep_assert_held(&q->sysfs_lock); if (q->elevator) { if (q->elevator->registered) elv_unregister_queue(q); ioc_clear_queue(q); elevator_exit(q, q->elevator); } ret = blk_mq_init_sched(q, new_e); if (ret) goto out; if (new_e) { ret = elv_register_queue(q, true); if (ret) { elevator_exit(q, q->elevator); goto out; } } if (new_e) blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name); else blk_add_trace_msg(q, "elv switch: none"); out: return ret; } static inline bool elv_support_iosched(struct request_queue *q) { if (!queue_is_mq(q) || (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED))) return false; return true; } /* * For single queue devices, default to using mq-deadline. If we have multiple * queues or mq-deadline is not available, default to "none". */ static struct elevator_type *elevator_get_default(struct request_queue *q) { if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT) return NULL; if (q->nr_hw_queues != 1 && !blk_mq_is_shared_tags(q->tag_set->flags)) return NULL; return elevator_get(q, "mq-deadline", false); } /* * Get the first elevator providing the features required by the request queue. * Default to "none" if no matching elevator is found. */ static struct elevator_type *elevator_get_by_features(struct request_queue *q) { struct elevator_type *e, *found = NULL; spin_lock(&elv_list_lock); list_for_each_entry(e, &elv_list, list) { if (elv_support_features(e->elevator_features, q->required_elevator_features)) { found = e; break; } } if (found && !try_module_get(found->elevator_owner)) found = NULL; spin_unlock(&elv_list_lock); return found; } /* * For a device queue that has no required features, use the default elevator * settings. Otherwise, use the first elevator available matching the required * features. If no suitable elevator is find or if the chosen elevator * initialization fails, fall back to the "none" elevator (no elevator). */ void elevator_init_mq(struct request_queue *q) { struct elevator_type *e; int err; if (!elv_support_iosched(q)) return; WARN_ON_ONCE(blk_queue_registered(q)); if (unlikely(q->elevator)) return; if (!q->required_elevator_features) e = elevator_get_default(q); else e = elevator_get_by_features(q); if (!e) return; /* * We are called before adding disk, when there isn't any FS I/O, * so freezing queue plus canceling dispatch work is enough to * drain any dispatch activities originated from passthrough * requests, then no need to quiesce queue which may add long boot * latency, especially when lots of disks are involved. */ blk_mq_freeze_queue(q); blk_mq_cancel_work_sync(q); err = blk_mq_init_sched(q, e); blk_mq_unfreeze_queue(q); if (err) { pr_warn("\"%s\" elevator initialization failed, " "falling back to \"none\"\n", e->elevator_name); elevator_put(e); } } /* * 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 int elevator_switch(struct request_queue *q, struct elevator_type *new_e) { int err; lockdep_assert_held(&q->sysfs_lock); blk_mq_freeze_queue(q); blk_mq_quiesce_queue(q); err = elevator_switch_mq(q, new_e); blk_mq_unquiesce_queue(q); blk_mq_unfreeze_queue(q); return err; } /* * Switch this queue to the given IO scheduler. */ static int __elevator_change(struct request_queue *q, const char *name) { char elevator_name[ELV_NAME_MAX]; struct elevator_type *e; /* Make sure queue is not in the middle of being removed */ if (!blk_queue_registered(q)) return -ENOENT; /* * Special case for mq, turn off scheduling */ if (!strncmp(name, "none", 4)) { if (!q->elevator) return 0; return elevator_switch(q, NULL); } strlcpy(elevator_name, name, sizeof(elevator_name)); e = elevator_get(q, strstrip(elevator_name), true); if (!e) return -EINVAL; if (q->elevator && elevator_match(q->elevator->type, elevator_name, 0)) { elevator_put(e); return 0; } return elevator_switch(q, e); } ssize_t elv_iosched_store(struct request_queue *q, const char *name, size_t count) { int ret; if (!elv_support_iosched(q)) return count; ret = __elevator_change(q, name); if (!ret) return count; return ret; } ssize_t elv_iosched_show(struct request_queue *q, char *name) { struct elevator_queue *e = q->elevator; struct elevator_type *elv = NULL; struct elevator_type *__e; int len = 0; if (!queue_is_mq(q)) return sprintf(name, "none\n"); if (!q->elevator) len += sprintf(name+len, "[none] "); else elv = e->type; spin_lock(&elv_list_lock); list_for_each_entry(__e, &elv_list, list) { if (elv && elevator_match(elv, __e->elevator_name, 0)) { len += sprintf(name+len, "[%s] ", elv->elevator_name); continue; } if (elv_support_iosched(q) && elevator_match(__e, __e->elevator_name, q->required_elevator_features)) len += sprintf(name+len, "%s ", __e->elevator_name); } spin_unlock(&elv_list_lock); if (q->elevator) len += sprintf(name+len, "none"); len += sprintf(len+name, "\n"); return len; } struct request *elv_rb_former_request(struct request_queue *q, struct request *rq) { struct rb_node *rbprev = rb_prev(&rq->rb_node); if (rbprev) return rb_entry_rq(rbprev); return NULL; } EXPORT_SYMBOL(elv_rb_former_request); struct request *elv_rb_latter_request(struct request_queue *q, struct request *rq) { struct rb_node *rbnext = rb_next(&rq->rb_node); if (rbnext) return rb_entry_rq(rbnext); return NULL; } EXPORT_SYMBOL(elv_rb_latter_request); static int __init elevator_setup(char *str) { pr_warn("Kernel parameter elevator= does not have any effect anymore.\n" "Please use sysfs to set IO scheduler for individual devices.\n"); return 1; } __setup("elevator=", elevator_setup);