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Linux currently has two models for block devices: - The classic request_fn based approach, where drivers use struct request units for IO. The block layer provides various helper functionalities to let drivers share code, things like tag management, timeout handling, queueing, etc. - The "stacked" approach, where a driver squeezes in between the block layer and IO submitter. Since this bypasses the IO stack, driver generally have to manage everything themselves. With drivers being written for new high IOPS devices, the classic request_fn based driver doesn't work well enough. The design dates back to when both SMP and high IOPS was rare. It has problems with scaling to bigger machines, and runs into scaling issues even on smaller machines when you have IOPS in the hundreds of thousands per device. The stacked approach is then most often selected as the model for the driver. But this means that everybody has to re-invent everything, and along with that we get all the problems again that the shared approach solved. This commit introduces blk-mq, block multi queue support. The design is centered around per-cpu queues for queueing IO, which then funnel down into x number of hardware submission queues. We might have a 1:1 mapping between the two, or it might be an N:M mapping. That all depends on what the hardware supports. blk-mq provides various helper functions, which include: - Scalable support for request tagging. Most devices need to be able to uniquely identify a request both in the driver and to the hardware. The tagging uses per-cpu caches for freed tags, to enable cache hot reuse. - Timeout handling without tracking request on a per-device basis. Basically the driver should be able to get a notification, if a request happens to fail. - Optional support for non 1:1 mappings between issue and submission queues. blk-mq can redirect IO completions to the desired location. - Support for per-request payloads. Drivers almost always need to associate a request structure with some driver private command structure. Drivers can tell blk-mq this at init time, and then any request handed to the driver will have the required size of memory associated with it. - Support for merging of IO, and plugging. The stacked model gets neither of these. Even for high IOPS devices, merging sequential IO reduces per-command overhead and thus increases bandwidth. For now, this is provided as a potential 3rd queueing model, with the hope being that, as it matures, it can replace both the classic and stacked model. That would get us back to having just 1 real model for block devices, leaving the stacked approach to dm/md devices (as it was originally intended). Contributions in this patch from the following people: Shaohua Li <shli@fusionio.com> Alexander Gordeev <agordeev@redhat.com> Christoph Hellwig <hch@infradead.org> Mike Christie <michaelc@cs.wisc.edu> Matias Bjorling <m@bjorling.me> Jeff Moyer <jmoyer@redhat.com> Acked-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
252 lines
7.8 KiB
C
252 lines
7.8 KiB
C
#ifndef BLK_INTERNAL_H
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#define BLK_INTERNAL_H
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#include <linux/idr.h>
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/* Amount of time in which a process may batch requests */
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#define BLK_BATCH_TIME (HZ/50UL)
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/* Number of requests a "batching" process may submit */
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#define BLK_BATCH_REQ 32
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extern struct kmem_cache *blk_requestq_cachep;
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extern struct kmem_cache *request_cachep;
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extern struct kobj_type blk_queue_ktype;
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extern struct ida blk_queue_ida;
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static inline void __blk_get_queue(struct request_queue *q)
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{
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kobject_get(&q->kobj);
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}
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int blk_init_rl(struct request_list *rl, struct request_queue *q,
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gfp_t gfp_mask);
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void blk_exit_rl(struct request_list *rl);
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void init_request_from_bio(struct request *req, struct bio *bio);
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void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
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struct bio *bio);
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int blk_rq_append_bio(struct request_queue *q, struct request *rq,
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struct bio *bio);
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void blk_queue_bypass_start(struct request_queue *q);
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void blk_queue_bypass_end(struct request_queue *q);
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void blk_dequeue_request(struct request *rq);
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void __blk_queue_free_tags(struct request_queue *q);
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bool __blk_end_bidi_request(struct request *rq, int error,
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unsigned int nr_bytes, unsigned int bidi_bytes);
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void blk_rq_timed_out_timer(unsigned long data);
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void blk_rq_check_expired(struct request *rq, unsigned long *next_timeout,
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unsigned int *next_set);
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void __blk_add_timer(struct request *req, struct list_head *timeout_list);
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void blk_delete_timer(struct request *);
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void blk_add_timer(struct request *);
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bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
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struct bio *bio);
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bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
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struct bio *bio);
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bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
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unsigned int *request_count);
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void blk_account_io_start(struct request *req, bool new_io);
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void blk_account_io_completion(struct request *req, unsigned int bytes);
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void blk_account_io_done(struct request *req);
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/*
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* Internal atomic flags for request handling
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*/
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enum rq_atomic_flags {
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REQ_ATOM_COMPLETE = 0,
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REQ_ATOM_STARTED,
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};
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/*
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* EH timer and IO completion will both attempt to 'grab' the request, make
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* sure that only one of them succeeds
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*/
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static inline int blk_mark_rq_complete(struct request *rq)
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{
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return test_and_set_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);
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}
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static inline void blk_clear_rq_complete(struct request *rq)
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{
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clear_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);
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}
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/*
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* Internal elevator interface
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*/
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#define ELV_ON_HASH(rq) hash_hashed(&(rq)->hash)
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void blk_insert_flush(struct request *rq);
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void blk_abort_flushes(struct request_queue *q);
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static inline struct request *__elv_next_request(struct request_queue *q)
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{
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struct request *rq;
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while (1) {
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if (!list_empty(&q->queue_head)) {
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rq = list_entry_rq(q->queue_head.next);
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return rq;
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}
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/*
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* Flush request is running and flush request isn't queueable
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* in the drive, we can hold the queue till flush request is
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* finished. Even we don't do this, driver can't dispatch next
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* requests and will requeue them. And this can improve
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* throughput too. For example, we have request flush1, write1,
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* flush 2. flush1 is dispatched, then queue is hold, write1
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* isn't inserted to queue. After flush1 is finished, flush2
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* will be dispatched. Since disk cache is already clean,
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* flush2 will be finished very soon, so looks like flush2 is
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* folded to flush1.
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* Since the queue is hold, a flag is set to indicate the queue
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* should be restarted later. Please see flush_end_io() for
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* details.
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*/
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if (q->flush_pending_idx != q->flush_running_idx &&
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!queue_flush_queueable(q)) {
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q->flush_queue_delayed = 1;
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return NULL;
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}
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if (unlikely(blk_queue_dying(q)) ||
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!q->elevator->type->ops.elevator_dispatch_fn(q, 0))
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return NULL;
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}
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}
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static inline void elv_activate_rq(struct request_queue *q, struct request *rq)
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{
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struct elevator_queue *e = q->elevator;
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if (e->type->ops.elevator_activate_req_fn)
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e->type->ops.elevator_activate_req_fn(q, rq);
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}
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static inline void elv_deactivate_rq(struct request_queue *q, struct request *rq)
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{
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struct elevator_queue *e = q->elevator;
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if (e->type->ops.elevator_deactivate_req_fn)
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e->type->ops.elevator_deactivate_req_fn(q, rq);
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}
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#ifdef CONFIG_FAIL_IO_TIMEOUT
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int blk_should_fake_timeout(struct request_queue *);
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ssize_t part_timeout_show(struct device *, struct device_attribute *, char *);
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ssize_t part_timeout_store(struct device *, struct device_attribute *,
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const char *, size_t);
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#else
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static inline int blk_should_fake_timeout(struct request_queue *q)
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{
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return 0;
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}
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#endif
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int ll_back_merge_fn(struct request_queue *q, struct request *req,
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struct bio *bio);
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int ll_front_merge_fn(struct request_queue *q, struct request *req,
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struct bio *bio);
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int attempt_back_merge(struct request_queue *q, struct request *rq);
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int attempt_front_merge(struct request_queue *q, struct request *rq);
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int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
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struct request *next);
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void blk_recalc_rq_segments(struct request *rq);
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void blk_rq_set_mixed_merge(struct request *rq);
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bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
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int blk_try_merge(struct request *rq, struct bio *bio);
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void blk_queue_congestion_threshold(struct request_queue *q);
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void __blk_run_queue_uncond(struct request_queue *q);
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int blk_dev_init(void);
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/*
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* Return the threshold (number of used requests) at which the queue is
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* considered to be congested. It include a little hysteresis to keep the
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* context switch rate down.
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*/
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static inline int queue_congestion_on_threshold(struct request_queue *q)
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{
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return q->nr_congestion_on;
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}
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/*
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* The threshold at which a queue is considered to be uncongested
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*/
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static inline int queue_congestion_off_threshold(struct request_queue *q)
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{
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return q->nr_congestion_off;
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}
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/*
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* Contribute to IO statistics IFF:
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*
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* a) it's attached to a gendisk, and
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* b) the queue had IO stats enabled when this request was started, and
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* c) it's a file system request
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*/
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static inline int blk_do_io_stat(struct request *rq)
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{
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return rq->rq_disk &&
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(rq->cmd_flags & REQ_IO_STAT) &&
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(rq->cmd_type == REQ_TYPE_FS);
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}
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/*
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* Internal io_context interface
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*/
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void get_io_context(struct io_context *ioc);
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struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q);
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struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
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gfp_t gfp_mask);
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void ioc_clear_queue(struct request_queue *q);
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int create_task_io_context(struct task_struct *task, gfp_t gfp_mask, int node);
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/**
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* create_io_context - try to create task->io_context
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* @gfp_mask: allocation mask
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* @node: allocation node
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*
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* If %current->io_context is %NULL, allocate a new io_context and install
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* it. Returns the current %current->io_context which may be %NULL if
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* allocation failed.
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*
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* Note that this function can't be called with IRQ disabled because
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* task_lock which protects %current->io_context is IRQ-unsafe.
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*/
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static inline struct io_context *create_io_context(gfp_t gfp_mask, int node)
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{
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WARN_ON_ONCE(irqs_disabled());
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if (unlikely(!current->io_context))
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create_task_io_context(current, gfp_mask, node);
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return current->io_context;
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}
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/*
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* Internal throttling interface
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*/
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#ifdef CONFIG_BLK_DEV_THROTTLING
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extern bool blk_throtl_bio(struct request_queue *q, struct bio *bio);
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extern void blk_throtl_drain(struct request_queue *q);
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extern int blk_throtl_init(struct request_queue *q);
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extern void blk_throtl_exit(struct request_queue *q);
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#else /* CONFIG_BLK_DEV_THROTTLING */
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static inline bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
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{
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return false;
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}
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static inline void blk_throtl_drain(struct request_queue *q) { }
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static inline int blk_throtl_init(struct request_queue *q) { return 0; }
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static inline void blk_throtl_exit(struct request_queue *q) { }
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#endif /* CONFIG_BLK_DEV_THROTTLING */
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#endif /* BLK_INTERNAL_H */
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