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, 368 insertions, 0 deletions

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
new file mode 100644
index 000000000000..26759798a0b3
--- /dev/null
+++ b/block/blk-mq-sched.c
@@ -0,0 +1,368 @@
+/*
+ * blk-mq scheduling framework
+ *
+ * Copyright (C) 2016 Jens Axboe
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/blk-mq.h>
+
+#include <trace/events/block.h>
+
+#include "blk.h"
+#include "blk-mq.h"
+#include "blk-mq-sched.h"
+#include "blk-mq-tag.h"
+#include "blk-wbt.h"
+
+void blk_mq_sched_free_hctx_data(struct request_queue *q,
+                                 void (*exit)(struct blk_mq_hw_ctx *))
+{
+        struct blk_mq_hw_ctx *hctx;
+        int i;
+
+        queue_for_each_hw_ctx(q, hctx, i) {
+                if (exit && hctx->sched_data)
+                        exit(hctx);
+                kfree(hctx->sched_data);
+                hctx->sched_data = NULL;
+        }
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
+
+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 *))
+{
+        struct blk_mq_hw_ctx *hctx;
+        int ret;
+        int i;
+
+        queue_for_each_hw_ctx(q, hctx, i) {
+                hctx->sched_data = kmalloc_node(size, GFP_KERNEL, hctx->numa_node);
+                if (!hctx->sched_data) {
+                        ret = -ENOMEM;
+                        goto error;
+                }
+
+                if (init) {
+                        ret = init(hctx);
+                        if (ret) {
+                                /*
+                                 * We don't want to give exit() a partially
+                                 * initialized sched_data. init() must clean up
+                                 * if it fails.
+                                 */
+                                kfree(hctx->sched_data);
+                                hctx->sched_data = NULL;
+                                goto error;
+                        }
+                }
+        }
+
+        return 0;
+error:
+        blk_mq_sched_free_hctx_data(q, exit);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_init_hctx_data);
+
+static void __blk_mq_sched_assign_ioc(struct request_queue *q,
+                                      struct request *rq, struct io_context *ioc)
+{
+        struct io_cq *icq;
+
+        spin_lock_irq(q->queue_lock);
+        icq = ioc_lookup_icq(ioc, q);
+        spin_unlock_irq(q->queue_lock);
+
+        if (!icq) {
+                icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
+                if (!icq)
+                        return;
+        }
+
+        rq->elv.icq = icq;
+        if (!blk_mq_sched_get_rq_priv(q, rq)) {
+                rq->rq_flags |= RQF_ELVPRIV;
+                get_io_context(icq->ioc);
+                return;
+        }
+
+        rq->elv.icq = NULL;
+}
+
+static void blk_mq_sched_assign_ioc(struct request_queue *q,
+                                    struct request *rq, struct bio *bio)
+{
+        struct io_context *ioc;
+
+        ioc = rq_ioc(bio);
+        if (ioc)
+                __blk_mq_sched_assign_ioc(q, rq, ioc);
+}
+
+struct request *blk_mq_sched_get_request(struct request_queue *q,
+                                         struct bio *bio,
+                                         unsigned int op,
+                                         struct blk_mq_alloc_data *data)
+{
+        struct elevator_queue *e = q->elevator;
+        struct blk_mq_hw_ctx *hctx;
+        struct blk_mq_ctx *ctx;
+        struct request *rq;
+        const bool is_flush = op & (REQ_PREFLUSH | REQ_FUA);
+
+        blk_queue_enter_live(q);
+        ctx = blk_mq_get_ctx(q);
+        hctx = blk_mq_map_queue(q, ctx->cpu);
+
+        blk_mq_set_alloc_data(data, q, 0, ctx, hctx);
+
+        if (e) {
+                data->flags |= BLK_MQ_REQ_INTERNAL;
+
+                /*
+                 * Flush requests are special and go directly to the
+                 * dispatch list.
+                 */
+                if (!is_flush && e->type->ops.mq.get_request) {
+                        rq = e->type->ops.mq.get_request(q, op, data);
+                        if (rq)
+                                rq->rq_flags |= RQF_QUEUED;
+                } else
+                        rq = __blk_mq_alloc_request(data, op);
+        } else {
+                rq = __blk_mq_alloc_request(data, op);
+                data->hctx->tags->rqs[rq->tag] = rq;
+        }
+
+        if (rq) {
+                if (!is_flush) {
+                        rq->elv.icq = NULL;
+                        if (e && e->type->icq_cache)
+                                blk_mq_sched_assign_ioc(q, rq, bio);
+                }
+                data->hctx->queued++;
+                return rq;
+        }
+
+        blk_queue_exit(q);
+        return NULL;
+}
+
+void blk_mq_sched_put_request(struct request *rq)
+{
+        struct request_queue *q = rq->q;
+        struct elevator_queue *e = q->elevator;
+
+        if (rq->rq_flags & RQF_ELVPRIV) {
+                blk_mq_sched_put_rq_priv(rq->q, rq);
+                if (rq->elv.icq) {
+                        put_io_context(rq->elv.icq->ioc);
+                        rq->elv.icq = NULL;
+                }
+        }
+
+        if ((rq->rq_flags & RQF_QUEUED) && e && e->type->ops.mq.put_request)
+                e->type->ops.mq.put_request(rq);
+        else
+                blk_mq_finish_request(rq);
+}
+
+void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
+{
+        struct elevator_queue *e = hctx->queue->elevator;
+        LIST_HEAD(rq_list);
+
+        if (unlikely(blk_mq_hctx_stopped(hctx)))
+                return;
+
+        hctx->run++;
+
+        /*
+         * If we have previous entries on our dispatch list, grab them first for
+         * more fair dispatch.
+         */
+        if (!list_empty_careful(&hctx->dispatch)) {
+                spin_lock(&hctx->lock);
+                if (!list_empty(&hctx->dispatch))
+                        list_splice_init(&hctx->dispatch, &rq_list);
+                spin_unlock(&hctx->lock);
+        }
+
+        /*
+         * Only ask the scheduler for requests, if we didn't have residual
+         * requests from the dispatch list. This is to avoid the case where
+         * we only ever dispatch a fraction of the requests available because
+         * of low device queue depth. Once we pull requests out of the IO
+         * scheduler, we can no longer merge or sort them. So it's best to
+         * leave them there for as long as we can. Mark the hw queue as
+         * needing a restart in that case.
+         */
+        if (list_empty(&rq_list)) {
+                if (e && e->type->ops.mq.dispatch_requests)
+                        e->type->ops.mq.dispatch_requests(hctx, &rq_list);
+                else
+                        blk_mq_flush_busy_ctxs(hctx, &rq_list);
+        } else
+                blk_mq_sched_mark_restart(hctx);
+
+        blk_mq_dispatch_rq_list(hctx, &rq_list);
+}
+
+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 *))
+{
+        do {
+                struct request *rq;
+
+                rq = get_rq(hctx);
+                if (!rq)
+                        break;
+
+                list_add_tail(&rq->queuelist, rq_list);
+        } while (1);
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_move_to_dispatch);
+
+bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio)
+{
+        struct request *rq;
+        int ret;
+
+        ret = elv_merge(q, &rq, bio);
+        if (ret == ELEVATOR_BACK_MERGE) {
+                if (!blk_mq_sched_allow_merge(q, rq, bio))
+                        return false;
+                if (bio_attempt_back_merge(q, rq, bio)) {
+                        if (!attempt_back_merge(q, rq))
+                                elv_merged_request(q, rq, ret);
+                        return true;
+                }
+        } else if (ret == ELEVATOR_FRONT_MERGE) {
+                if (!blk_mq_sched_allow_merge(q, rq, bio))
+                        return false;
+                if (bio_attempt_front_merge(q, rq, bio)) {
+                        if (!attempt_front_merge(q, rq))
+                                elv_merged_request(q, rq, ret);
+                        return true;
+                }
+        }
+
+        return false;
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
+
+bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
+{
+        struct elevator_queue *e = q->elevator;
+
+        if (e->type->ops.mq.bio_merge) {
+                struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
+                struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
+
+                blk_mq_put_ctx(ctx);
+                return e->type->ops.mq.bio_merge(hctx, bio);
+        }
+
+        return false;
+}
+
+bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
+{
+        return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
+
+void blk_mq_sched_request_inserted(struct request *rq)
+{
+        trace_block_rq_insert(rq->q, rq);
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
+
+bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx, struct request *rq)
+{
+        if (rq->tag == -1) {
+                rq->rq_flags |= RQF_SORTED;
+                return false;
+        }
+
+        /*
+         * If we already have a real request tag, send directly to
+         * the dispatch list.
+         */
+        spin_lock(&hctx->lock);
+        list_add(&rq->queuelist, &hctx->dispatch);
+        spin_unlock(&hctx->lock);
+        return true;
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_bypass_insert);
+
+static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
+                                   struct blk_mq_hw_ctx *hctx,
+                                   unsigned int hctx_idx)
+{
+        if (hctx->sched_tags) {
+                blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
+                blk_mq_free_rq_map(hctx->sched_tags);
+                hctx->sched_tags = NULL;
+        }
+}
+
+int blk_mq_sched_setup(struct request_queue *q)
+{
+        struct blk_mq_tag_set *set = q->tag_set;
+        struct blk_mq_hw_ctx *hctx;
+        int ret, i;
+
+        /*
+         * Default to 256, since we don't split into sync/async like the
+         * old code did. Additionally, this is a per-hw queue depth.
+         */
+        q->nr_requests = 2 * BLKDEV_MAX_RQ;
+
+        /*
+         * We're switching to using an IO scheduler, so setup the hctx
+         * scheduler tags and switch the request map from the regular
+         * tags to scheduler tags. First allocate what we need, so we
+         * can safely fail and fallback, if needed.
+         */
+        ret = 0;
+        queue_for_each_hw_ctx(q, hctx, i) {
+                hctx->sched_tags = blk_mq_alloc_rq_map(set, i, q->nr_requests, 0);
+                if (!hctx->sched_tags) {
+                        ret = -ENOMEM;
+                        break;
+                }
+                ret = blk_mq_alloc_rqs(set, hctx->sched_tags, i, q->nr_requests);
+                if (ret)
+                        break;
+        }
+
+        /*
+         * If we failed, free what we did allocate
+         */
+        if (ret) {
+                queue_for_each_hw_ctx(q, hctx, i) {
+                        if (!hctx->sched_tags)
+                                continue;
+                        blk_mq_sched_free_tags(set, hctx, i);
+                }
+
+                return ret;
+        }
+
+        return 0;
+}
+
+void blk_mq_sched_teardown(struct request_queue *q)
+{
+        struct blk_mq_tag_set *set = q->tag_set;
+        struct blk_mq_hw_ctx *hctx;
+        int i;
+
+        queue_for_each_hw_ctx(q, hctx, i)
+                blk_mq_sched_free_tags(set, hctx, i);
+}