Merge tag 'f2fs-for-4.18' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk...

[linux-2.6/btrfs-unstable.git] / block / kyber-iosched.c

/*
 * The Kyber I/O scheduler. Controls latency by throttling queue depths using
 * scalable techniques.
 *
 * Copyright (C) 2017 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/blk-mq.h>
#include <linux/elevator.h>
#include <linux/module.h>
#include <linux/sbitmap.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-debugfs.h"
#include "blk-mq-sched.h"
#include "blk-mq-tag.h"
#include "blk-stat.h"

/* Scheduling domains. */
enum {
        KYBER_READ,
        KYBER_SYNC_WRITE,
        KYBER_OTHER, /* Async writes, discard, etc. */
        KYBER_NUM_DOMAINS,
};

enum {
        KYBER_MIN_DEPTH = 256,

        /*
         * In order to prevent starvation of synchronous requests by a flood of
         * asynchronous requests, we reserve 25% of requests for synchronous
         * operations.
         */
        KYBER_ASYNC_PERCENT = 75,
};

/*
 * Initial device-wide depths for each scheduling domain.
 *
 * Even for fast devices with lots of tags like NVMe, you can saturate
 * the device with only a fraction of the maximum possible queue depth.
 * So, we cap these to a reasonable value.
 */
static const unsigned int kyber_depth[] = {
        [KYBER_READ] = 256,
        [KYBER_SYNC_WRITE] = 128,
        [KYBER_OTHER] = 64,
};

/*
 * Scheduling domain batch sizes. We favor reads.
 */
static const unsigned int kyber_batch_size[] = {
        [KYBER_READ] = 16,
        [KYBER_SYNC_WRITE] = 8,
        [KYBER_OTHER] = 8,
};

/*
 * There is a same mapping between ctx & hctx and kcq & khd,
 * we use request->mq_ctx->index_hw to index the kcq in khd.
 */
struct kyber_ctx_queue {
        /*
         * Used to ensure operations on rq_list and kcq_map to be an atmoic one.
         * Also protect the rqs on rq_list when merge.
         */
        spinlock_t lock;
        struct list_head rq_list[KYBER_NUM_DOMAINS];
} ____cacheline_aligned_in_smp;

struct kyber_queue_data {
        struct request_queue *q;

        struct blk_stat_callback *cb;

        /*
         * The device is divided into multiple scheduling domains based on the
         * request type. Each domain has a fixed number of in-flight requests of
         * that type device-wide, limited by these tokens.
         */
        struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];

        /*
         * Async request percentage, converted to per-word depth for
         * sbitmap_get_shallow().
         */
        unsigned int async_depth;

        /* Target latencies in nanoseconds. */
        u64 read_lat_nsec, write_lat_nsec;
};

struct kyber_hctx_data {
        spinlock_t lock;
        struct list_head rqs[KYBER_NUM_DOMAINS];
        unsigned int cur_domain;
        unsigned int batching;
        struct kyber_ctx_queue *kcqs;
        struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
        wait_queue_entry_t domain_wait[KYBER_NUM_DOMAINS];
        struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
        atomic_t wait_index[KYBER_NUM_DOMAINS];
};

static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
                             void *key);

static unsigned int kyber_sched_domain(unsigned int op)
{
        if ((op & REQ_OP_MASK) == REQ_OP_READ)
                return KYBER_READ;
        else if ((op & REQ_OP_MASK) == REQ_OP_WRITE && op_is_sync(op))
                return KYBER_SYNC_WRITE;
        else
                return KYBER_OTHER;
}

enum {
        NONE = 0,
        GOOD = 1,
        GREAT = 2,
        BAD = -1,
        AWFUL = -2,
};

#define IS_GOOD(status) ((status) > 0)
#define IS_BAD(status) ((status) < 0)

static int kyber_lat_status(struct blk_stat_callback *cb,
                            unsigned int sched_domain, u64 target)
{
        u64 latency;

        if (!cb->stat[sched_domain].nr_samples)
                return NONE;

        latency = cb->stat[sched_domain].mean;
        if (latency >= 2 * target)
                return AWFUL;
        else if (latency > target)
                return BAD;
        else if (latency <= target / 2)
                return GREAT;
        else /* (latency <= target) */
                return GOOD;
}

/*
 * Adjust the read or synchronous write depth given the status of reads and
 * writes. The goal is that the latencies of the two domains are fair (i.e., if
 * one is good, then the other is good).
 */
static void kyber_adjust_rw_depth(struct kyber_queue_data *kqd,
                                  unsigned int sched_domain, int this_status,
                                  int other_status)
{
        unsigned int orig_depth, depth;

        /*
         * If this domain had no samples, or reads and writes are both good or
         * both bad, don't adjust the depth.
         */
        if (this_status == NONE ||
            (IS_GOOD(this_status) && IS_GOOD(other_status)) ||
            (IS_BAD(this_status) && IS_BAD(other_status)))
                return;

        orig_depth = depth = kqd->domain_tokens[sched_domain].sb.depth;

        if (other_status == NONE) {
                depth++;
        } else {
                switch (this_status) {
                case GOOD:
                        if (other_status == AWFUL)
                                depth -= max(depth / 4, 1U);
                        else
                                depth -= max(depth / 8, 1U);
                        break;
                case GREAT:
                        if (other_status == AWFUL)
                                depth /= 2;
                        else
                                depth -= max(depth / 4, 1U);
                        break;
                case BAD:
                        depth++;
                        break;
                case AWFUL:
                        if (other_status == GREAT)
                                depth += 2;
                        else
                                depth++;
                        break;
                }
        }

        depth = clamp(depth, 1U, kyber_depth[sched_domain]);
        if (depth != orig_depth)
                sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
}

/*
 * Adjust the depth of other requests given the status of reads and synchronous
 * writes. As long as either domain is doing fine, we don't throttle, but if
 * both domains are doing badly, we throttle heavily.
 */
static void kyber_adjust_other_depth(struct kyber_queue_data *kqd,
                                     int read_status, int write_status,
                                     bool have_samples)
{
        unsigned int orig_depth, depth;
        int status;

        orig_depth = depth = kqd->domain_tokens[KYBER_OTHER].sb.depth;

        if (read_status == NONE && write_status == NONE) {
                depth += 2;
        } else if (have_samples) {
                if (read_status == NONE)
                        status = write_status;
                else if (write_status == NONE)
                        status = read_status;
                else
                        status = max(read_status, write_status);
                switch (status) {
                case GREAT:
                        depth += 2;
                        break;
                case GOOD:
                        depth++;
                        break;
                case BAD:
                        depth -= max(depth / 4, 1U);
                        break;
                case AWFUL:
                        depth /= 2;
                        break;
                }
        }

        depth = clamp(depth, 1U, kyber_depth[KYBER_OTHER]);
        if (depth != orig_depth)
                sbitmap_queue_resize(&kqd->domain_tokens[KYBER_OTHER], depth);
}

/*
 * Apply heuristics for limiting queue depths based on gathered latency
 * statistics.
 */
static void kyber_stat_timer_fn(struct blk_stat_callback *cb)
{
        struct kyber_queue_data *kqd = cb->data;
        int read_status, write_status;

        read_status = kyber_lat_status(cb, KYBER_READ, kqd->read_lat_nsec);
        write_status = kyber_lat_status(cb, KYBER_SYNC_WRITE, kqd->write_lat_nsec);

        kyber_adjust_rw_depth(kqd, KYBER_READ, read_status, write_status);
        kyber_adjust_rw_depth(kqd, KYBER_SYNC_WRITE, write_status, read_status);
        kyber_adjust_other_depth(kqd, read_status, write_status,
                                 cb->stat[KYBER_OTHER].nr_samples != 0);

        /*
         * Continue monitoring latencies if we aren't hitting the targets or
         * we're still throttling other requests.
         */
        if (!blk_stat_is_active(kqd->cb) &&
            ((IS_BAD(read_status) || IS_BAD(write_status) ||
              kqd->domain_tokens[KYBER_OTHER].sb.depth < kyber_depth[KYBER_OTHER])))
                blk_stat_activate_msecs(kqd->cb, 100);
}

static unsigned int kyber_sched_tags_shift(struct kyber_queue_data *kqd)
{
        /*
         * All of the hardware queues have the same depth, so we can just grab
         * the shift of the first one.
         */
        return kqd->q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
}

static int kyber_bucket_fn(const struct request *rq)
{
        return kyber_sched_domain(rq->cmd_flags);
}

static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
{
        struct kyber_queue_data *kqd;
        unsigned int max_tokens;
        unsigned int shift;
        int ret = -ENOMEM;
        int i;

        kqd = kmalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
        if (!kqd)
                goto err;
        kqd->q = q;

        kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, kyber_bucket_fn,
                                          KYBER_NUM_DOMAINS, kqd);
        if (!kqd->cb)
                goto err_kqd;

        /*
         * The maximum number of tokens for any scheduling domain is at least
         * the queue depth of a single hardware queue. If the hardware doesn't
         * have many tags, still provide a reasonable number.
         */
        max_tokens = max_t(unsigned int, q->tag_set->queue_depth,
                           KYBER_MIN_DEPTH);
        for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
                WARN_ON(!kyber_depth[i]);
                WARN_ON(!kyber_batch_size[i]);
                ret = sbitmap_queue_init_node(&kqd->domain_tokens[i],
                                              max_tokens, -1, false, GFP_KERNEL,
                                              q->node);
                if (ret) {
                        while (--i >= 0)
                                sbitmap_queue_free(&kqd->domain_tokens[i]);
                        goto err_cb;
                }
                sbitmap_queue_resize(&kqd->domain_tokens[i], kyber_depth[i]);
        }

        shift = kyber_sched_tags_shift(kqd);
        kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;

        kqd->read_lat_nsec = 2000000ULL;
        kqd->write_lat_nsec = 10000000ULL;

        return kqd;

err_cb:
        blk_stat_free_callback(kqd->cb);
err_kqd:
        kfree(kqd);
err:
        return ERR_PTR(ret);
}

static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)
{
        struct kyber_queue_data *kqd;
        struct elevator_queue *eq;

        eq = elevator_alloc(q, e);
        if (!eq)
                return -ENOMEM;

        kqd = kyber_queue_data_alloc(q);
        if (IS_ERR(kqd)) {
                kobject_put(&eq->kobj);
                return PTR_ERR(kqd);
        }

        eq->elevator_data = kqd;
        q->elevator = eq;

        blk_stat_add_callback(q, kqd->cb);

        return 0;
}

static void kyber_exit_sched(struct elevator_queue *e)
{
        struct kyber_queue_data *kqd = e->elevator_data;
        struct request_queue *q = kqd->q;
        int i;

        blk_stat_remove_callback(q, kqd->cb);

        for (i = 0; i < KYBER_NUM_DOMAINS; i++)
                sbitmap_queue_free(&kqd->domain_tokens[i]);
        blk_stat_free_callback(kqd->cb);
        kfree(kqd);
}

static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
{
        unsigned int i;

        spin_lock_init(&kcq->lock);
        for (i = 0; i < KYBER_NUM_DOMAINS; i++)
                INIT_LIST_HEAD(&kcq->rq_list[i]);
}

static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
{
        struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
        struct kyber_hctx_data *khd;
        int i;

        khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
        if (!khd)
                return -ENOMEM;

        khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
                                       sizeof(struct kyber_ctx_queue),
                                       GFP_KERNEL, hctx->numa_node);
        if (!khd->kcqs)
                goto err_khd;

        for (i = 0; i < hctx->nr_ctx; i++)
                kyber_ctx_queue_init(&khd->kcqs[i]);

        for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
                if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
                                      ilog2(8), GFP_KERNEL, hctx->numa_node)) {
                        while (--i >= 0)
                                sbitmap_free(&khd->kcq_map[i]);
                        goto err_kcqs;
                }
        }

        spin_lock_init(&khd->lock);

        for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
                INIT_LIST_HEAD(&khd->rqs[i]);
                init_waitqueue_func_entry(&khd->domain_wait[i],
                                          kyber_domain_wake);
                khd->domain_wait[i].private = hctx;
                INIT_LIST_HEAD(&khd->domain_wait[i].entry);
                atomic_set(&khd->wait_index[i], 0);
        }

        khd->cur_domain = 0;
        khd->batching = 0;

        hctx->sched_data = khd;
        sbitmap_queue_min_shallow_depth(&hctx->sched_tags->bitmap_tags,
                                        kqd->async_depth);

        return 0;

err_kcqs:
        kfree(khd->kcqs);
err_khd:
        kfree(khd);
        return -ENOMEM;
}

static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
{
        struct kyber_hctx_data *khd = hctx->sched_data;
        int i;

        for (i = 0; i < KYBER_NUM_DOMAINS; i++)
                sbitmap_free(&khd->kcq_map[i]);
        kfree(khd->kcqs);
        kfree(hctx->sched_data);
}

static int rq_get_domain_token(struct request *rq)
{
        return (long)rq->elv.priv[0];
}

static void rq_set_domain_token(struct request *rq, int token)
{
        rq->elv.priv[0] = (void *)(long)token;
}

static void rq_clear_domain_token(struct kyber_queue_data *kqd,
                                  struct request *rq)
{
        unsigned int sched_domain;
        int nr;

        nr = rq_get_domain_token(rq);
        if (nr != -1) {
                sched_domain = kyber_sched_domain(rq->cmd_flags);
                sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
                                    rq->mq_ctx->cpu);
        }
}

static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
{
        /*
         * We use the scheduler tags as per-hardware queue queueing tokens.
         * Async requests can be limited at this stage.
         */
        if (!op_is_sync(op)) {
                struct kyber_queue_data *kqd = data->q->elevator->elevator_data;

                data->shallow_depth = kqd->async_depth;
        }
}

static bool kyber_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
{
        struct kyber_hctx_data *khd = hctx->sched_data;
        struct blk_mq_ctx *ctx = blk_mq_get_ctx(hctx->queue);
        struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw];
        unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
        struct list_head *rq_list = &kcq->rq_list[sched_domain];
        bool merged;

        spin_lock(&kcq->lock);
        merged = blk_mq_bio_list_merge(hctx->queue, rq_list, bio);
        spin_unlock(&kcq->lock);
        blk_mq_put_ctx(ctx);

        return merged;
}

static void kyber_prepare_request(struct request *rq, struct bio *bio)
{
        rq_set_domain_token(rq, -1);
}

static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
                                  struct list_head *rq_list, bool at_head)
{
        struct kyber_hctx_data *khd = hctx->sched_data;
        struct request *rq, *next;

        list_for_each_entry_safe(rq, next, rq_list, queuelist) {
                unsigned int sched_domain = kyber_sched_domain(rq->cmd_flags);
                struct kyber_ctx_queue *kcq = &khd->kcqs[rq->mq_ctx->index_hw];
                struct list_head *head = &kcq->rq_list[sched_domain];

                spin_lock(&kcq->lock);
                if (at_head)
                        list_move(&rq->queuelist, head);
                else
                        list_move_tail(&rq->queuelist, head);
                sbitmap_set_bit(&khd->kcq_map[sched_domain],
                                rq->mq_ctx->index_hw);
                blk_mq_sched_request_inserted(rq);
                spin_unlock(&kcq->lock);
        }
}

static void kyber_finish_request(struct request *rq)
{
        struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;

        rq_clear_domain_token(kqd, rq);
}

static void kyber_completed_request(struct request *rq)
{
        struct request_queue *q = rq->q;
        struct kyber_queue_data *kqd = q->elevator->elevator_data;
        unsigned int sched_domain;
        u64 now, latency, target;

        /*
         * Check if this request met our latency goal. If not, quickly gather
         * some statistics and start throttling.
         */
        sched_domain = kyber_sched_domain(rq->cmd_flags);
        switch (sched_domain) {
        case KYBER_READ:
                target = kqd->read_lat_nsec;
                break;
        case KYBER_SYNC_WRITE:
                target = kqd->write_lat_nsec;
                break;
        default:
                return;
        }

        /* If we are already monitoring latencies, don't check again. */
        if (blk_stat_is_active(kqd->cb))
                return;

        now = ktime_get_ns();
        if (now < rq->io_start_time_ns)
                return;

        latency = now - rq->io_start_time_ns;

        if (latency > target)
                blk_stat_activate_msecs(kqd->cb, 10);
}

struct flush_kcq_data {
        struct kyber_hctx_data *khd;
        unsigned int sched_domain;
        struct list_head *list;
};

static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
{
        struct flush_kcq_data *flush_data = data;
        struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];

        spin_lock(&kcq->lock);
        list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
                              flush_data->list);
        sbitmap_clear_bit(sb, bitnr);
        spin_unlock(&kcq->lock);

        return true;
}

static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
                                  unsigned int sched_domain,
                                  struct list_head *list)
{
        struct flush_kcq_data data = {
                .khd = khd,
                .sched_domain = sched_domain,
                .list = list,
        };

        sbitmap_for_each_set(&khd->kcq_map[sched_domain],
                             flush_busy_kcq, &data);
}

static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
                             void *key)
{
        struct blk_mq_hw_ctx *hctx = READ_ONCE(wait->private);

        list_del_init(&wait->entry);
        blk_mq_run_hw_queue(hctx, true);
        return 1;
}

static int kyber_get_domain_token(struct kyber_queue_data *kqd,
                                  struct kyber_hctx_data *khd,
                                  struct blk_mq_hw_ctx *hctx)
{
        unsigned int sched_domain = khd->cur_domain;
        struct sbitmap_queue *domain_tokens = &kqd->domain_tokens[sched_domain];
        wait_queue_entry_t *wait = &khd->domain_wait[sched_domain];
        struct sbq_wait_state *ws;
        int nr;

        nr = __sbitmap_queue_get(domain_tokens);

        /*
         * If we failed to get a domain token, make sure the hardware queue is
         * run when one becomes available. Note that this is serialized on
         * khd->lock, but we still need to be careful about the waker.
         */
        if (nr < 0 && list_empty_careful(&wait->entry)) {
                ws = sbq_wait_ptr(domain_tokens,
                                  &khd->wait_index[sched_domain]);
                khd->domain_ws[sched_domain] = ws;
                add_wait_queue(&ws->wait, wait);

                /*
                 * Try again in case a token was freed before we got on the wait
                 * queue.
                 */
                nr = __sbitmap_queue_get(domain_tokens);
        }

        /*
         * If we got a token while we were on the wait queue, remove ourselves
         * from the wait queue to ensure that all wake ups make forward
         * progress. It's possible that the waker already deleted the entry
         * between the !list_empty_careful() check and us grabbing the lock, but
         * list_del_init() is okay with that.
         */
        if (nr >= 0 && !list_empty_careful(&wait->entry)) {
                ws = khd->domain_ws[sched_domain];
                spin_lock_irq(&ws->wait.lock);
                list_del_init(&wait->entry);
                spin_unlock_irq(&ws->wait.lock);
        }

        return nr;
}

static struct request *
kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
                          struct kyber_hctx_data *khd,
                          struct blk_mq_hw_ctx *hctx)
{
        struct list_head *rqs;
        struct request *rq;
        int nr;

        rqs = &khd->rqs[khd->cur_domain];

        /*
         * If we already have a flushed request, then we just need to get a
         * token for it. Otherwise, if there are pending requests in the kcqs,
         * flush the kcqs, but only if we can get a token. If not, we should
         * leave the requests in the kcqs so that they can be merged. Note that
         * khd->lock serializes the flushes, so if we observed any bit set in
         * the kcq_map, we will always get a request.
         */
        rq = list_first_entry_or_null(rqs, struct request, queuelist);
        if (rq) {
                nr = kyber_get_domain_token(kqd, khd, hctx);
                if (nr >= 0) {
                        khd->batching++;
                        rq_set_domain_token(rq, nr);
                        list_del_init(&rq->queuelist);
                        return rq;
                }
        } else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
                nr = kyber_get_domain_token(kqd, khd, hctx);
                if (nr >= 0) {
                        kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
                        rq = list_first_entry(rqs, struct request, queuelist);
                        khd->batching++;
                        rq_set_domain_token(rq, nr);
                        list_del_init(&rq->queuelist);
                        return rq;
                }
        }

        /* There were either no pending requests or no tokens. */
        return NULL;
}

static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
        struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
        struct kyber_hctx_data *khd = hctx->sched_data;
        struct request *rq;
        int i;

        spin_lock(&khd->lock);

        /*
         * First, if we are still entitled to batch, try to dispatch a request
         * from the batch.
         */
        if (khd->batching < kyber_batch_size[khd->cur_domain]) {
                rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
                if (rq)
                        goto out;
        }

        /*
         * Either,
         * 1. We were no longer entitled to a batch.
         * 2. The domain we were batching didn't have any requests.
         * 3. The domain we were batching was out of tokens.
         *
         * Start another batch. Note that this wraps back around to the original
         * domain if no other domains have requests or tokens.
         */
        khd->batching = 0;
        for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
                if (khd->cur_domain == KYBER_NUM_DOMAINS - 1)
                        khd->cur_domain = 0;
                else
                        khd->cur_domain++;

                rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
                if (rq)
                        goto out;
        }

        rq = NULL;
out:
        spin_unlock(&khd->lock);
        return rq;
}

static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
{
        struct kyber_hctx_data *khd = hctx->sched_data;
        int i;

        for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
                if (!list_empty_careful(&khd->rqs[i]) ||
                    sbitmap_any_bit_set(&khd->kcq_map[i]))
                        return true;
        }

        return false;
}

#define KYBER_LAT_SHOW_STORE(op)                                        \
static ssize_t kyber_##op##_lat_show(struct elevator_queue *e,          \
                                     char *page)                        \
{                                                                       \
        struct kyber_queue_data *kqd = e->elevator_data;                \
                                                                        \
        return sprintf(page, "%llu\n", kqd->op##_lat_nsec);             \
}                                                                       \
                                                                        \
static ssize_t kyber_##op##_lat_store(struct elevator_queue *e,         \
                                      const char *page, size_t count)   \
{                                                                       \
        struct kyber_queue_data *kqd = e->elevator_data;                \
        unsigned long long nsec;                                        \
        int ret;                                                        \
                                                                        \
        ret = kstrtoull(page, 10, &nsec);                               \
        if (ret)                                                        \
                return ret;                                             \
                                                                        \
        kqd->op##_lat_nsec = nsec;                                      \
                                                                        \
        return count;                                                   \
}
KYBER_LAT_SHOW_STORE(read);
KYBER_LAT_SHOW_STORE(write);
#undef KYBER_LAT_SHOW_STORE

#define KYBER_LAT_ATTR(op) __ATTR(op##_lat_nsec, 0644, kyber_##op##_lat_show, kyber_##op##_lat_store)
static struct elv_fs_entry kyber_sched_attrs[] = {
        KYBER_LAT_ATTR(read),
        KYBER_LAT_ATTR(write),
        __ATTR_NULL
};
#undef KYBER_LAT_ATTR

#ifdef CONFIG_BLK_DEBUG_FS
#define KYBER_DEBUGFS_DOMAIN_ATTRS(domain, name)                        \
static int kyber_##name##_tokens_show(void *data, struct seq_file *m)   \
{                                                                       \
        struct request_queue *q = data;                                 \
        struct kyber_queue_data *kqd = q->elevator->elevator_data;      \
                                                                        \
        sbitmap_queue_show(&kqd->domain_tokens[domain], m);             \
        return 0;                                                       \
}                                                                       \
                                                                        \
static void *kyber_##name##_rqs_start(struct seq_file *m, loff_t *pos)  \
        __acquires(&khd->lock)                                          \
{                                                                       \
        struct blk_mq_hw_ctx *hctx = m->private;                        \
        struct kyber_hctx_data *khd = hctx->sched_data;                 \
                                                                        \
        spin_lock(&khd->lock);                                          \
        return seq_list_start(&khd->rqs[domain], *pos);                 \
}                                                                       \
                                                                        \
static void *kyber_##name##_rqs_next(struct seq_file *m, void *v,       \
                                     loff_t *pos)                       \
{                                                                       \
        struct blk_mq_hw_ctx *hctx = m->private;                        \
        struct kyber_hctx_data *khd = hctx->sched_data;                 \
                                                                        \
        return seq_list_next(v, &khd->rqs[domain], pos);                \
}                                                                       \
                                                                        \
static void kyber_##name##_rqs_stop(struct seq_file *m, void *v)        \
        __releases(&khd->lock)                                          \
{                                                                       \
        struct blk_mq_hw_ctx *hctx = m->private;                        \
        struct kyber_hctx_data *khd = hctx->sched_data;                 \
                                                                        \
        spin_unlock(&khd->lock);                                        \
}                                                                       \
                                                                        \
static const struct seq_operations kyber_##name##_rqs_seq_ops = {       \
        .start  = kyber_##name##_rqs_start,                             \
        .next   = kyber_##name##_rqs_next,                              \
        .stop   = kyber_##name##_rqs_stop,                              \
        .show   = blk_mq_debugfs_rq_show,                               \
};                                                                      \
                                                                        \
static int kyber_##name##_waiting_show(void *data, struct seq_file *m)  \
{                                                                       \
        struct blk_mq_hw_ctx *hctx = data;                              \
        struct kyber_hctx_data *khd = hctx->sched_data;                 \
        wait_queue_entry_t *wait = &khd->domain_wait[domain];           \
                                                                        \
        seq_printf(m, "%d\n", !list_empty_careful(&wait->entry));       \
        return 0;                                                       \
}
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_SYNC_WRITE, sync_write)
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_OTHER, other)
#undef KYBER_DEBUGFS_DOMAIN_ATTRS

static int kyber_async_depth_show(void *data, struct seq_file *m)
{
        struct request_queue *q = data;
        struct kyber_queue_data *kqd = q->elevator->elevator_data;

        seq_printf(m, "%u\n", kqd->async_depth);
        return 0;
}

static int kyber_cur_domain_show(void *data, struct seq_file *m)
{
        struct blk_mq_hw_ctx *hctx = data;
        struct kyber_hctx_data *khd = hctx->sched_data;

        switch (khd->cur_domain) {
        case KYBER_READ:
                seq_puts(m, "READ\n");
                break;
        case KYBER_SYNC_WRITE:
                seq_puts(m, "SYNC_WRITE\n");
                break;
        case KYBER_OTHER:
                seq_puts(m, "OTHER\n");
                break;
        default:
                seq_printf(m, "%u\n", khd->cur_domain);
                break;
        }
        return 0;
}

static int kyber_batching_show(void *data, struct seq_file *m)
{
        struct blk_mq_hw_ctx *hctx = data;
        struct kyber_hctx_data *khd = hctx->sched_data;

        seq_printf(m, "%u\n", khd->batching);
        return 0;
}

#define KYBER_QUEUE_DOMAIN_ATTRS(name)  \
        {#name "_tokens", 0400, kyber_##name##_tokens_show}
static const struct blk_mq_debugfs_attr kyber_queue_debugfs_attrs[] = {
        KYBER_QUEUE_DOMAIN_ATTRS(read),
        KYBER_QUEUE_DOMAIN_ATTRS(sync_write),
        KYBER_QUEUE_DOMAIN_ATTRS(other),
        {"async_depth", 0400, kyber_async_depth_show},
        {},
};
#undef KYBER_QUEUE_DOMAIN_ATTRS

#define KYBER_HCTX_DOMAIN_ATTRS(name)                                   \
        {#name "_rqs", 0400, .seq_ops = &kyber_##name##_rqs_seq_ops},   \
        {#name "_waiting", 0400, kyber_##name##_waiting_show}
static const struct blk_mq_debugfs_attr kyber_hctx_debugfs_attrs[] = {
        KYBER_HCTX_DOMAIN_ATTRS(read),
        KYBER_HCTX_DOMAIN_ATTRS(sync_write),
        KYBER_HCTX_DOMAIN_ATTRS(other),
        {"cur_domain", 0400, kyber_cur_domain_show},
        {"batching", 0400, kyber_batching_show},
        {},
};
#undef KYBER_HCTX_DOMAIN_ATTRS
#endif

static struct elevator_type kyber_sched = {
        .ops.mq = {
                .init_sched = kyber_init_sched,
                .exit_sched = kyber_exit_sched,
                .init_hctx = kyber_init_hctx,
                .exit_hctx = kyber_exit_hctx,
                .limit_depth = kyber_limit_depth,
                .bio_merge = kyber_bio_merge,
                .prepare_request = kyber_prepare_request,
                .insert_requests = kyber_insert_requests,
                .finish_request = kyber_finish_request,
                .requeue_request = kyber_finish_request,
                .completed_request = kyber_completed_request,
                .dispatch_request = kyber_dispatch_request,
                .has_work = kyber_has_work,
        },
        .uses_mq = true,
#ifdef CONFIG_BLK_DEBUG_FS
        .queue_debugfs_attrs = kyber_queue_debugfs_attrs,
        .hctx_debugfs_attrs = kyber_hctx_debugfs_attrs,
#endif
        .elevator_attrs = kyber_sched_attrs,
        .elevator_name = "kyber",
        .elevator_owner = THIS_MODULE,
};

static int __init kyber_init(void)
{
        return elv_register(&kyber_sched);
}

static void __exit kyber_exit(void)
{
        elv_unregister(&kyber_sched);
}

module_init(kyber_init);
module_exit(kyber_exit);

MODULE_AUTHOR("Omar Sandoval");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Kyber I/O scheduler");