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author | Jens Axboe <axboe@kernel.dk> | 2013-10-24 09:20:05 +0100 |
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committer | Jens Axboe <axboe@kernel.dk> | 2013-10-25 11:56:00 +0100 |
commit | 320ae51feed5c2f13664aa05a76bec198967e04d (patch) | |
tree | ad37ccbcc5ddb1c9c19e48965bf8fec1b05217dc /include/linux/blk-mq.h | |
parent | 1dddc01af0d42b21058e0cb9c1ca9e8d5204d9b0 (diff) | |
download | linux-stable-320ae51feed5c2f13664aa05a76bec198967e04d.tar.gz linux-stable-320ae51feed5c2f13664aa05a76bec198967e04d.tar.bz2 linux-stable-320ae51feed5c2f13664aa05a76bec198967e04d.zip |
blk-mq: new multi-queue block IO queueing mechanism
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>
Diffstat (limited to 'include/linux/blk-mq.h')
-rw-r--r-- | include/linux/blk-mq.h | 182 |
1 files changed, 182 insertions, 0 deletions
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h new file mode 100644 index 000000000000..746042ff321a --- /dev/null +++ b/include/linux/blk-mq.h @@ -0,0 +1,182 @@ +#ifndef BLK_MQ_H +#define BLK_MQ_H + +#include <linux/blkdev.h> + +struct blk_mq_tags; + +struct blk_mq_cpu_notifier { + struct list_head list; + void *data; + void (*notify)(void *data, unsigned long action, unsigned int cpu); +}; + +struct blk_mq_hw_ctx { + struct { + spinlock_t lock; + struct list_head dispatch; + } ____cacheline_aligned_in_smp; + + unsigned long state; /* BLK_MQ_S_* flags */ + struct delayed_work delayed_work; + + unsigned long flags; /* BLK_MQ_F_* flags */ + + struct request_queue *queue; + unsigned int queue_num; + + void *driver_data; + + unsigned int nr_ctx; + struct blk_mq_ctx **ctxs; + unsigned int nr_ctx_map; + unsigned long *ctx_map; + + struct request **rqs; + struct list_head page_list; + struct blk_mq_tags *tags; + + unsigned long queued; + unsigned long run; +#define BLK_MQ_MAX_DISPATCH_ORDER 10 + unsigned long dispatched[BLK_MQ_MAX_DISPATCH_ORDER]; + + unsigned int queue_depth; + unsigned int numa_node; + unsigned int cmd_size; /* per-request extra data */ + + struct blk_mq_cpu_notifier cpu_notifier; + struct kobject kobj; +}; + +struct blk_mq_reg { + struct blk_mq_ops *ops; + unsigned int nr_hw_queues; + unsigned int queue_depth; + unsigned int reserved_tags; + unsigned int cmd_size; /* per-request extra data */ + int numa_node; + unsigned int timeout; + unsigned int flags; /* BLK_MQ_F_* */ +}; + +typedef int (queue_rq_fn)(struct blk_mq_hw_ctx *, struct request *); +typedef struct blk_mq_hw_ctx *(map_queue_fn)(struct request_queue *, const int); +typedef struct blk_mq_hw_ctx *(alloc_hctx_fn)(struct blk_mq_reg *,unsigned int); +typedef void (free_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int); +typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int); +typedef void (exit_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int); + +struct blk_mq_ops { + /* + * Queue request + */ + queue_rq_fn *queue_rq; + + /* + * Map to specific hardware queue + */ + map_queue_fn *map_queue; + + /* + * Called on request timeout + */ + rq_timed_out_fn *timeout; + + /* + * Override for hctx allocations (should probably go) + */ + alloc_hctx_fn *alloc_hctx; + free_hctx_fn *free_hctx; + + /* + * Called when the block layer side of a hardware queue has been + * set up, allowing the driver to allocate/init matching structures. + * Ditto for exit/teardown. + */ + init_hctx_fn *init_hctx; + exit_hctx_fn *exit_hctx; +}; + +enum { + BLK_MQ_RQ_QUEUE_OK = 0, /* queued fine */ + BLK_MQ_RQ_QUEUE_BUSY = 1, /* requeue IO for later */ + BLK_MQ_RQ_QUEUE_ERROR = 2, /* end IO with error */ + + BLK_MQ_F_SHOULD_MERGE = 1 << 0, + BLK_MQ_F_SHOULD_SORT = 1 << 1, + BLK_MQ_F_SHOULD_IPI = 1 << 2, + + BLK_MQ_S_STOPPED = 1 << 0, + + BLK_MQ_MAX_DEPTH = 2048, +}; + +struct request_queue *blk_mq_init_queue(struct blk_mq_reg *, void *); +void blk_mq_free_queue(struct request_queue *); +int blk_mq_register_disk(struct gendisk *); +void blk_mq_unregister_disk(struct gendisk *); +void blk_mq_init_commands(struct request_queue *, void (*init)(void *data, struct blk_mq_hw_ctx *, struct request *, unsigned int), void *data); + +void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule); + +void blk_mq_insert_request(struct request_queue *, struct request *, bool); +void blk_mq_run_queues(struct request_queue *q, bool async); +void blk_mq_free_request(struct request *rq); +bool blk_mq_can_queue(struct blk_mq_hw_ctx *); +struct request *blk_mq_alloc_request(struct request_queue *q, int rw, gfp_t gfp); +struct request *blk_mq_alloc_reserved_request(struct request_queue *q, int rw, gfp_t gfp); +struct request *blk_mq_rq_from_tag(struct request_queue *q, unsigned int tag); + +struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *, const int ctx_index); +struct blk_mq_hw_ctx *blk_mq_alloc_single_hw_queue(struct blk_mq_reg *, unsigned int); +void blk_mq_free_single_hw_queue(struct blk_mq_hw_ctx *, unsigned int); + +void blk_mq_end_io(struct request *rq, int error); + +void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx); +void blk_mq_start_hw_queue(struct blk_mq_hw_ctx *hctx); +void blk_mq_start_stopped_hw_queues(struct request_queue *q); + +/* + * Driver command data is immediately after the request. So subtract request + * size to get back to the original request. + */ +static inline struct request *blk_mq_rq_from_pdu(void *pdu) +{ + return pdu - sizeof(struct request); +} +static inline void *blk_mq_rq_to_pdu(struct request *rq) +{ + return (void *) rq + sizeof(*rq); +} + +static inline struct request *blk_mq_tag_to_rq(struct blk_mq_hw_ctx *hctx, + unsigned int tag) +{ + return hctx->rqs[tag]; +} + +#define queue_for_each_hw_ctx(q, hctx, i) \ + for ((i) = 0, hctx = (q)->queue_hw_ctx[0]; \ + (i) < (q)->nr_hw_queues; (i)++, hctx = (q)->queue_hw_ctx[i]) + +#define queue_for_each_ctx(q, ctx, i) \ + for ((i) = 0, ctx = per_cpu_ptr((q)->queue_ctx, 0); \ + (i) < (q)->nr_queues; (i)++, ctx = per_cpu_ptr(q->queue_ctx, (i))) + +#define hctx_for_each_ctx(hctx, ctx, i) \ + for ((i) = 0, ctx = (hctx)->ctxs[0]; \ + (i) < (hctx)->nr_ctx; (i)++, ctx = (hctx)->ctxs[(i)]) + +#define blk_ctx_sum(q, sum) \ +({ \ + struct blk_mq_ctx *__x; \ + unsigned int __ret = 0, __i; \ + \ + queue_for_each_ctx((q), __x, __i) \ + __ret += sum; \ + __ret; \ +}) + +#endif |