blk-mq-sched: add framework for MQ capable IO schedulers

This adds a set of hooks that intercepts the blk-mq path of
allocating/inserting/issuing/completing requests, allowing
us to develop a scheduler within that framework.

We reuse the existing elevator scheduler API on the registration
side, but augment that with the scheduler flagging support for
the blk-mq interfce, and with a separate set of ops hooks for MQ
devices.

We split driver and scheduler tags, so we can run the scheduling
independently of device queue depth.

Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>

1 files changed, 170 insertions, 0 deletions

diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
new file mode 100644
index 000000000000..35c49e2e008a
--- /dev/null
+++ b/block/blk-mq-sched.h
@@ -0,0 +1,170 @@
+#ifndef BLK_MQ_SCHED_H
+#define BLK_MQ_SCHED_H
+
+#include "blk-mq.h"
+#include "blk-mq-tag.h"
+
+int blk_mq_sched_init_hctx_data(struct request_queue *q, size_t size,
+                                int (*init)(struct blk_mq_hw_ctx *),
+                                void (*exit)(struct blk_mq_hw_ctx *));
+
+void blk_mq_sched_free_hctx_data(struct request_queue *q,
+                                 void (*exit)(struct blk_mq_hw_ctx *));
+
+struct request *blk_mq_sched_get_request(struct request_queue *q, struct bio *bio, unsigned int op, struct blk_mq_alloc_data *data);
+void blk_mq_sched_put_request(struct request *rq);
+
+void blk_mq_sched_request_inserted(struct request *rq);
+bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx, struct request *rq);
+bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio);
+bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio);
+bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq);
+
+void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
+void blk_mq_sched_move_to_dispatch(struct blk_mq_hw_ctx *hctx,
+                        struct list_head *rq_list,
+                        struct request *(*get_rq)(struct blk_mq_hw_ctx *));
+
+int blk_mq_sched_setup(struct request_queue *q);
+void blk_mq_sched_teardown(struct request_queue *q);
+
+static inline bool
+blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
+{
+        struct elevator_queue *e = q->elevator;
+
+        if (!e || blk_queue_nomerges(q) || !bio_mergeable(bio))
+                return false;
+
+        return __blk_mq_sched_bio_merge(q, bio);
+}
+
+static inline int blk_mq_sched_get_rq_priv(struct request_queue *q,
+                                           struct request *rq)
+{
+        struct elevator_queue *e = q->elevator;
+
+        if (e && e->type->ops.mq.get_rq_priv)
+                return e->type->ops.mq.get_rq_priv(q, rq);
+
+        return 0;
+}
+
+static inline void blk_mq_sched_put_rq_priv(struct request_queue *q,
+                                            struct request *rq)
+{
+        struct elevator_queue *e = q->elevator;
+
+        if (e && e->type->ops.mq.put_rq_priv)
+                e->type->ops.mq.put_rq_priv(q, rq);
+}
+
+static inline void
+blk_mq_sched_insert_request(struct request *rq, bool at_head, bool run_queue,
+                            bool async)
+{
+        struct request_queue *q = rq->q;
+        struct elevator_queue *e = q->elevator;
+        struct blk_mq_ctx *ctx = rq->mq_ctx;
+        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
+
+        if (e && e->type->ops.mq.insert_requests) {
+                LIST_HEAD(list);
+
+                list_add(&rq->queuelist, &list);
+                e->type->ops.mq.insert_requests(hctx, &list, at_head);
+        } else {
+                spin_lock(&ctx->lock);
+                __blk_mq_insert_request(hctx, rq, at_head);
+                spin_unlock(&ctx->lock);
+        }
+
+        if (run_queue)
+                blk_mq_run_hw_queue(hctx, async);
+}
+
+static inline void
+blk_mq_sched_insert_requests(struct request_queue *q, struct blk_mq_ctx *ctx,
+                             struct list_head *list, bool run_queue_async)
+{
+        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
+        struct elevator_queue *e = hctx->queue->elevator;
+
+        if (e && e->type->ops.mq.insert_requests)
+                e->type->ops.mq.insert_requests(hctx, list, false);
+        else
+                blk_mq_insert_requests(hctx, ctx, list);
+
+        blk_mq_run_hw_queue(hctx, run_queue_async);
+}
+
+static inline bool
+blk_mq_sched_allow_merge(struct request_queue *q, struct request *rq,
+                         struct bio *bio)
+{
+        struct elevator_queue *e = q->elevator;
+
+        if (e && e->type->ops.mq.allow_merge)
+                return e->type->ops.mq.allow_merge(q, rq, bio);
+
+        return true;
+}
+
+static inline void
+blk_mq_sched_completed_request(struct blk_mq_hw_ctx *hctx, struct request *rq)
+{
+        struct elevator_queue *e = hctx->queue->elevator;
+
+        if (e && e->type->ops.mq.completed_request)
+                e->type->ops.mq.completed_request(hctx, rq);
+
+        BUG_ON(rq->internal_tag == -1);
+
+        blk_mq_put_tag(hctx, hctx->sched_tags, rq->mq_ctx, rq->internal_tag);
+
+        if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state)) {
+                clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
+                blk_mq_run_hw_queue(hctx, true);
+        }
+}
+
+static inline void blk_mq_sched_started_request(struct request *rq)
+{
+        struct request_queue *q = rq->q;
+        struct elevator_queue *e = q->elevator;
+
+        if (e && e->type->ops.mq.started_request)
+                e->type->ops.mq.started_request(rq);
+}
+
+static inline void blk_mq_sched_requeue_request(struct request *rq)
+{
+        struct request_queue *q = rq->q;
+        struct elevator_queue *e = q->elevator;
+
+        if (e && e->type->ops.mq.requeue_request)
+                e->type->ops.mq.requeue_request(rq);
+}
+
+static inline bool blk_mq_sched_has_work(struct blk_mq_hw_ctx *hctx)
+{
+        struct elevator_queue *e = hctx->queue->elevator;
+
+        if (e && e->type->ops.mq.has_work)
+                return e->type->ops.mq.has_work(hctx);
+
+        return false;
+}
+
+static inline void blk_mq_sched_mark_restart(struct blk_mq_hw_ctx *hctx)
+{
+        if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
+                set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
+}
+
+static inline bool blk_mq_sched_needs_restart(struct blk_mq_hw_ctx *hctx)
+{
+        return test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
+}
+
+#endif