// SPDX-License-Identifier: GPL-2.0

  /*
   * The Kyber I/O scheduler. Controls latency by throttling queue depths using
   * scalable techniques.
   *
   * Copyright (C) 2017 Facebook

   */
  
  #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"

  #define CREATE_TRACE_POINTS
  #include <trace/events/kyber.h>

  /*
   * Scheduling domains: the device is divided into multiple domains based on the
   * request type.
   */

  enum {
  	KYBER_READ,

  	KYBER_WRITE,
  	KYBER_DISCARD,
  	KYBER_OTHER,

  	KYBER_NUM_DOMAINS,
  };

  static const char *kyber_domain_names[] = {
  	[KYBER_READ] = "READ",
  	[KYBER_WRITE] = "WRITE",
  	[KYBER_DISCARD] = "DISCARD",
  	[KYBER_OTHER] = "OTHER",
  };

  enum {

  	/*
  	 * 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,
  };
  
  /*

   * Maximum device-wide depth 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_WRITE] = 128,
  	[KYBER_DISCARD] = 64,
  	[KYBER_OTHER] = 16,

  };
  
  /*

   * Default latency targets for each scheduling domain.
   */
  static const u64 kyber_latency_targets[] = {

  	[KYBER_READ] = 2ULL * NSEC_PER_MSEC,
  	[KYBER_WRITE] = 10ULL * NSEC_PER_MSEC,
  	[KYBER_DISCARD] = 5ULL * NSEC_PER_SEC,

  };
  
  /*
   * Batch size (number of requests we'll dispatch in a row) for each scheduling
   * domain.

   */
  static const unsigned int kyber_batch_size[] = {
  	[KYBER_READ] = 16,

  	[KYBER_WRITE] = 8,
  	[KYBER_DISCARD] = 1,
  	[KYBER_OTHER] = 1,
  };
  
  /*
   * Requests latencies are recorded in a histogram with buckets defined relative
   * to the target latency:
   *
   * <= 1/4 * target latency
   * <= 1/2 * target latency
   * <= 3/4 * target latency
   * <= target latency
   * <= 1 1/4 * target latency
   * <= 1 1/2 * target latency
   * <= 1 3/4 * target latency
   * > 1 3/4 * target latency
   */
  enum {
  	/*
  	 * The width of the latency histogram buckets is
  	 * 1 / (1 << KYBER_LATENCY_SHIFT) * target latency.
  	 */
  	KYBER_LATENCY_SHIFT = 2,
  	/*
  	 * The first (1 << KYBER_LATENCY_SHIFT) buckets are <= target latency,
  	 * thus, "good".
  	 */
  	KYBER_GOOD_BUCKETS = 1 << KYBER_LATENCY_SHIFT,
  	/* There are also (1 << KYBER_LATENCY_SHIFT) "bad" buckets. */
  	KYBER_LATENCY_BUCKETS = 2 << KYBER_LATENCY_SHIFT,
  };
  
  /*
   * We measure both the total latency and the I/O latency (i.e., latency after
   * submitting to the device).
   */
  enum {
  	KYBER_TOTAL_LATENCY,
  	KYBER_IO_LATENCY,
  };

  static const char *kyber_latency_type_names[] = {
  	[KYBER_TOTAL_LATENCY] = "total",
  	[KYBER_IO_LATENCY] = "I/O",
  };

  /*
   * Per-cpu latency histograms: total latency and I/O latency for each scheduling
   * domain except for KYBER_OTHER.
   */
  struct kyber_cpu_latency {
  	atomic_t buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];

  };

  /*
   * 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;

  	/*

  	 * Each scheduling domain has a limited number of in-flight requests
  	 * 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;

  	struct kyber_cpu_latency __percpu *cpu_latency;
  
  	/* Timer for stats aggregation and adjusting domain tokens. */
  	struct timer_list timer;
  
  	unsigned int latency_buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
  
  	unsigned long latency_timeout[KYBER_OTHER];
  
  	int domain_p99[KYBER_OTHER];

  	/* Target latencies in nanoseconds. */

  	u64 latency_targets[KYBER_OTHER];

  };
  
  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];

  	struct sbq_wait 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)

  {

  	switch (op & REQ_OP_MASK) {
  	case REQ_OP_READ:

  		return KYBER_READ;

  	case REQ_OP_WRITE:
  		return KYBER_WRITE;
  	case REQ_OP_DISCARD:
  		return KYBER_DISCARD;
  	default:

  		return KYBER_OTHER;

  	}

  }

  static void flush_latency_buckets(struct kyber_queue_data *kqd,
  				  struct kyber_cpu_latency *cpu_latency,
  				  unsigned int sched_domain, unsigned int type)

  {

  	unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
  	atomic_t *cpu_buckets = cpu_latency->buckets[sched_domain][type];
  	unsigned int bucket;

  	for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
  		buckets[bucket] += atomic_xchg(&cpu_buckets[bucket], 0);

  }
  
  /*

   * Calculate the histogram bucket with the given percentile rank, or -1 if there
   * aren't enough samples yet.

   */

  static int calculate_percentile(struct kyber_queue_data *kqd,
  				unsigned int sched_domain, unsigned int type,
  				unsigned int percentile)

  {

  	unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
  	unsigned int bucket, samples = 0, percentile_samples;
  
  	for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
  		samples += buckets[bucket];
  
  	if (!samples)
  		return -1;

  
  	/*

  	 * We do the calculation once we have 500 samples or one second passes
  	 * since the first sample was recorded, whichever comes first.

  	 */

  	if (!kqd->latency_timeout[sched_domain])
  		kqd->latency_timeout[sched_domain] = max(jiffies + HZ, 1UL);
  	if (samples < 500 &&
  	    time_is_after_jiffies(kqd->latency_timeout[sched_domain])) {
  		return -1;
  	}
  	kqd->latency_timeout[sched_domain] = 0;

  	percentile_samples = DIV_ROUND_UP(samples * percentile, 100);
  	for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS - 1; bucket++) {
  		if (buckets[bucket] >= percentile_samples)

  			break;

  		percentile_samples -= buckets[bucket];

  	}

  	memset(buckets, 0, sizeof(kqd->latency_buckets[sched_domain][type]));

  	trace_kyber_latency(kqd->q, kyber_domain_names[sched_domain],
  			    kyber_latency_type_names[type], percentile,
  			    bucket + 1, 1 << KYBER_LATENCY_SHIFT, samples);

  	return bucket;
  }
  
  static void kyber_resize_domain(struct kyber_queue_data *kqd,
  				unsigned int sched_domain, unsigned int depth)
  {

  	depth = clamp(depth, 1U, kyber_depth[sched_domain]);

  	if (depth != kqd->domain_tokens[sched_domain].sb.depth) {

  		sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);

  		trace_kyber_adjust(kqd->q, kyber_domain_names[sched_domain],
  				   depth);
  	}

  }

  static void kyber_timer_fn(struct timer_list *t)
  {
  	struct kyber_queue_data *kqd = from_timer(kqd, t, timer);
  	unsigned int sched_domain;
  	int cpu;
  	bool bad = false;
  
  	/* Sum all of the per-cpu latency histograms. */
  	for_each_online_cpu(cpu) {
  		struct kyber_cpu_latency *cpu_latency;
  
  		cpu_latency = per_cpu_ptr(kqd->cpu_latency, cpu);
  		for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
  			flush_latency_buckets(kqd, cpu_latency, sched_domain,
  					      KYBER_TOTAL_LATENCY);
  			flush_latency_buckets(kqd, cpu_latency, sched_domain,
  					      KYBER_IO_LATENCY);

  		}
  	}

  	/*
  	 * Check if any domains have a high I/O latency, which might indicate
  	 * congestion in the device. Note that we use the p90; we don't want to
  	 * be too sensitive to outliers here.
  	 */
  	for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
  		int p90;

  		p90 = calculate_percentile(kqd, sched_domain, KYBER_IO_LATENCY,
  					   90);
  		if (p90 >= KYBER_GOOD_BUCKETS)
  			bad = true;
  	}

  
  	/*

  	 * Adjust the scheduling domain depths. If we determined that there was
  	 * congestion, we throttle all domains with good latencies. Either way,
  	 * we ease up on throttling domains with bad latencies.

  	 */

  	for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
  		unsigned int orig_depth, depth;
  		int p99;
  
  		p99 = calculate_percentile(kqd, sched_domain,
  					   KYBER_TOTAL_LATENCY, 99);
  		/*
  		 * This is kind of subtle: different domains will not
  		 * necessarily have enough samples to calculate the latency
  		 * percentiles during the same window, so we have to remember
  		 * the p99 for the next time we observe congestion; once we do,
  		 * we don't want to throttle again until we get more data, so we
  		 * reset it to -1.
  		 */
  		if (bad) {
  			if (p99 < 0)
  				p99 = kqd->domain_p99[sched_domain];
  			kqd->domain_p99[sched_domain] = -1;
  		} else if (p99 >= 0) {
  			kqd->domain_p99[sched_domain] = p99;
  		}
  		if (p99 < 0)
  			continue;
  
  		/*
  		 * If this domain has bad latency, throttle less. Otherwise,
  		 * throttle more iff we determined that there is congestion.
  		 *
  		 * The new depth is scaled linearly with the p99 latency vs the
  		 * latency target. E.g., if the p99 is 3/4 of the target, then
  		 * we throttle down to 3/4 of the current depth, and if the p99
  		 * is 2x the target, then we double the depth.
  		 */
  		if (bad || p99 >= KYBER_GOOD_BUCKETS) {
  			orig_depth = kqd->domain_tokens[sched_domain].sb.depth;
  			depth = (orig_depth * (p99 + 1)) >> KYBER_LATENCY_SHIFT;
  			kyber_resize_domain(kqd, sched_domain, depth);
  		}
  	}

  }

  static unsigned int kyber_sched_tags_shift(struct request_queue *q)

  {
  	/*
  	 * All of the hardware queues have the same depth, so we can just grab
  	 * the shift of the first one.
  	 */

  	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags->sb.shift;

  }

  static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
  {
  	struct kyber_queue_data *kqd;

  	unsigned int shift;
  	int ret = -ENOMEM;
  	int i;

  	kqd = kzalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);

  	if (!kqd)
  		goto err;

  	kqd->q = q;

  	kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency,
  					    GFP_KERNEL | __GFP_ZERO);
  	if (!kqd->cpu_latency)

  		goto err_kqd;

  	timer_setup(&kqd->timer, kyber_timer_fn, 0);

  	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],

  					      kyber_depth[i], -1, false,
  					      GFP_KERNEL, q->node);

  		if (ret) {
  			while (--i >= 0)
  				sbitmap_queue_free(&kqd->domain_tokens[i]);

  			goto err_buckets;

  		}

  	}

  	for (i = 0; i < KYBER_OTHER; i++) {
  		kqd->domain_p99[i] = -1;
  		kqd->latency_targets[i] = kyber_latency_targets[i];
  	}

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

  
  	return kqd;

  err_buckets:
  	free_percpu(kqd->cpu_latency);

  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);
  	}

  	blk_stat_enable_accounting(q);

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

  	return 0;
  }
  
  static void kyber_exit_sched(struct elevator_queue *e)
  {
  	struct kyber_queue_data *kqd = e->elevator_data;

  	int i;

  	del_timer_sync(&kqd->timer);

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

  	free_percpu(kqd->cpu_latency);

  	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]);

  		khd->domain_wait[i].sbq = NULL;
  		init_waitqueue_func_entry(&khd->domain_wait[i].wait,

  					  kyber_domain_wake);

  		khd->domain_wait[i].wait.private = hctx;
  		INIT_LIST_HEAD(&khd->domain_wait[i].wait.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,
  		unsigned int nr_segs)

  {
  	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[hctx->type]];

  	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_bio_list_merge(hctx->queue, rq_list, bio, nr_segs);

  	spin_unlock(&kcq->lock);

  
  	return merged;
  }

  static void kyber_prepare_request(struct request *rq)

  {
  	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[hctx->type]];

  		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[hctx->type]);

  		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 add_latency_sample(struct kyber_cpu_latency *cpu_latency,
  			       unsigned int sched_domain, unsigned int type,
  			       u64 target, u64 latency)

  {

  	unsigned int bucket;
  	u64 divisor;

  	if (latency > 0) {
  		divisor = max_t(u64, target >> KYBER_LATENCY_SHIFT, 1);
  		bucket = min_t(unsigned int, div64_u64(latency - 1, divisor),
  			       KYBER_LATENCY_BUCKETS - 1);
  	} else {
  		bucket = 0;

  	}

  	atomic_inc(&cpu_latency->buckets[sched_domain][type][bucket]);
  }

  static void kyber_completed_request(struct request *rq, u64 now)
  {
  	struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
  	struct kyber_cpu_latency *cpu_latency;
  	unsigned int sched_domain;
  	u64 target;
  
  	sched_domain = kyber_sched_domain(rq->cmd_flags);
  	if (sched_domain == KYBER_OTHER)

  		return;

  	cpu_latency = get_cpu_ptr(kqd->cpu_latency);
  	target = kqd->latency_targets[sched_domain];
  	add_latency_sample(cpu_latency, sched_domain, KYBER_TOTAL_LATENCY,
  			   target, now - rq->start_time_ns);
  	add_latency_sample(cpu_latency, sched_domain, KYBER_IO_LATENCY, target,
  			   now - rq->io_start_time_ns);
  	put_cpu_ptr(kqd->cpu_latency);

  	timer_reduce(&kqd->timer, jiffies + HZ / 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 *wqe, unsigned mode, int flags,

  			     void *key)
  {

  	struct blk_mq_hw_ctx *hctx = READ_ONCE(wqe->private);
  	struct sbq_wait *wait = container_of(wqe, struct sbq_wait, wait);

  	sbitmap_del_wait_queue(wait);

  	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];

  	struct sbq_wait *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->wait.entry)) {

  		ws = sbq_wait_ptr(domain_tokens,
  				  &khd->wait_index[sched_domain]);

  		khd->domain_ws[sched_domain] = ws;

  		sbitmap_add_wait_queue(domain_tokens, ws, 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->wait.entry)) {

  		ws = khd->domain_ws[sched_domain];
  		spin_lock_irq(&ws->wait.lock);

  		sbitmap_del_wait_queue(wait);

  		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 {
  			trace_kyber_throttled(kqd->q,
  					      kyber_domain_names[khd->cur_domain]);

  		}

  	} 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;

  		} else {
  			trace_kyber_throttled(kqd->q,
  					      kyber_domain_names[khd->cur_domain]);

  		}

  	}
  
  	/* 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(domain, name)				\
  static ssize_t kyber_##name##_lat_show(struct elevator_queue *e,	\
  				       char *page)			\

  {									\
  	struct kyber_queue_data *kqd = e->elevator_data;		\
  									\

  	return sprintf(page, "%llu
  ", kqd->latency_targets[domain]);	\

  }									\
  									\

  static ssize_t kyber_##name##_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->latency_targets[domain] = nsec;				\

  									\
  	return count;							\
  }

  KYBER_LAT_SHOW_STORE(KYBER_READ, read);
  KYBER_LAT_SHOW_STORE(KYBER_WRITE, 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].wait;	\

  									\

  	seq_printf(m, "%d
  ", !list_empty_careful(&wait->entry));	\

  	return 0;							\
  }
  KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)

  KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_WRITE, write)
  KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_DISCARD, discard)

  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
  ", 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;

  	seq_printf(m, "%s
  ", kyber_domain_names[khd->cur_domain]);

  	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
  ", 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(write),
  	KYBER_QUEUE_DOMAIN_ATTRS(discard),

  	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(write),
  	KYBER_HCTX_DOMAIN_ATTRS(discard),

  	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 = {

  		.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,
  	},

  #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");