// SPDX-License-Identifier: GPL-2.0
/*
* Block device elevator/IO-scheduler.
*
* Copyright (C) 2000 Andrea Arcangeli <[email protected]> SuSE
*
* 30042000 Jens Axboe <[email protected]> :
*
* 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 <[email protected]> :
* 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 <trace/events/block.h>
#include "elevator.h"
#include "blk.h"
#include "blk-mq-sched.h"
#include "blk-pm.h"
#include "blk-wbt.h"
#include "blk-cgroup.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 bool 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 true;
}
/*
* 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);
/**
* elevator_match - Check whether @e's name or alias matches @name
* @e: Scheduler to test
* @name: Elevator name to test
*
* Return true if the elevator @e's name or alias matches @name.
*/
static bool elevator_match(const struct elevator_type *e, const char *name)
{
return !strcmp(e->elevator_name, name) ||
(e->elevator_alias && !strcmp(e->elevator_alias, name));
}
static struct elevator_type *__elevator_find(const char *name)
{
struct elevator_type *e;
list_for_each_entry(e, &elv_list, list)
if (elevator_match(e, name))
return e;
return NULL;
}
static struct elevator_type *elevator_find_get(struct request_queue *q,
const char *name)
{
struct elevator_type *e;
spin_lock(&elv_list_lock);
e = __elevator_find(name);
if (e && (!elevator_tryget(e)))
e = NULL;
spin_unlock(&elv_list_lock);
return e;
}
static const 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;
__elevator_get(e);
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 = q->elevator;
ioc_clear_queue(q);
blk_mq_sched_free_rqs(q);
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 const 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->disk->queue_kobj, "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);
set_bit(ELEVATOR_FLAG_REGISTERED, &e->flags);
}
return error;
}
void elv_unregister_queue(struct request_queue *q)
{
struct elevator_queue *e = q->elevator;
lockdep_assert_held(&q->sysfs_lock);
if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) {
kobject_uevent(&e->kobj, KOBJ_REMOVE);
kobject_del(&e->kobj);
}
}
int elv_register(struct elevator_type *e)
{
/* finish request is mandatory */
if (WARN_ON_ONCE(!e->ops.finish_request))
return -EINVAL;
/* 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)) {
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);
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_find_get(q, "mq-deadline");
}
/*
* Use the default elevator settings. 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;
e = elevator_get_default(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.
*
* If switching fails, we are most likely running out of memory and not able
* to restore the old io scheduler, so leaving the io scheduler being none.
*/
int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
{
int ret;
lockdep_assert_held(&q->sysfs_lock);
blk_mq_freeze_queue(q);
blk_mq_quiesce_queue(q);
if (q->elevator) {
elv_unregister_queue(q);
elevator_exit(q);
}
ret = blk_mq_init_sched(q, new_e);
if (ret)
goto out_unfreeze;
ret = elv_register_queue(q, true);
if (ret) {
elevator_exit(q);
goto out_unfreeze;
}
blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
out_unfreeze:
blk_mq_unquiesce_queue(q);
blk_mq_unfreeze_queue(q);
if (ret) {
pr_warn("elv: switch to \"%s\" failed, falling back to \"none\"\n",
new_e->elevator_name);
}
return ret;
}
void elevator_disable(struct request_queue *q)
{
lockdep_assert_held(&q->sysfs_lock);
blk_mq_freeze_queue(q);
blk_mq_quiesce_queue(q);
elv_unregister_queue(q);
elevator_exit(q);
blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
q->elevator = NULL;
q->nr_requests = q->tag_set->queue_depth;
blk_add_trace_msg(q, "elv switch: none");
blk_mq_unquiesce_queue(q);
blk_mq_unfreeze_queue(q);
}
/*
* Switch this queue to the given IO scheduler.
*/
static int elevator_change(struct request_queue *q, const char *elevator_name)
{
struct elevator_type *e;
int ret;
/* Make sure queue is not in the middle of being removed */
if (!blk_queue_registered(q))
return -ENOENT;
if (!strncmp(elevator_name, "none", 4)) {
if (q->elevator)
elevator_disable(q);
return 0;
}
if (q->elevator && elevator_match(q->elevator->type, elevator_name))
return 0;
e = elevator_find_get(q, elevator_name);
if (!e)
return -EINVAL;
ret = elevator_switch(q, e);
elevator_put(e);
return ret;
}
int elv_iosched_load_module(struct gendisk *disk, const char *buf,
size_t count)
{
char elevator_name[ELV_NAME_MAX];
if (!elv_support_iosched(disk->queue))
return -EOPNOTSUPP;
strscpy(elevator_name, buf, sizeof(elevator_name));
request_module("%s-iosched", strstrip(elevator_name));
return 0;
}
ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
size_t count)
{
char elevator_name[ELV_NAME_MAX];
int ret;
if (!elv_support_iosched(disk->queue))
return count;
strscpy(elevator_name, buf, sizeof(elevator_name));
ret = elevator_change(disk->queue, strstrip(elevator_name));
if (!ret)
return count;
return ret;
}
ssize_t elv_iosched_show(struct gendisk *disk, char *name)
{
struct request_queue *q = disk->queue;
struct elevator_queue *eq = q->elevator;
struct elevator_type *cur = NULL, *e;
int len = 0;
if (!elv_support_iosched(q))
return sprintf(name, "none\n");
if (!q->elevator) {
len += sprintf(name+len, "[none] ");
} else {
len += sprintf(name+len, "none ");
cur = eq->type;
}
spin_lock(&elv_list_lock);
list_for_each_entry(e, &elv_list, list) {
if (e == cur)
len += sprintf(name+len, "[%s] ", e->elevator_name);
else
len += sprintf(name+len, "%s ", e->elevator_name);
}
spin_unlock(&elv_list_lock);
len += sprintf(name+len, "\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);
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