/*
   * Block stat tracking code
   *
   * Copyright (C) 2016 Jens Axboe
   */
  #include <linux/kernel.h>

  #include <linux/rculist.h>

  #include <linux/blk-mq.h>
  
  #include "blk-stat.h"
  #include "blk-mq.h"

  #include "blk.h"

  #define BLK_RQ_STAT_BATCH	64

  struct blk_queue_stats {
  	struct list_head callbacks;
  	spinlock_t lock;

  	bool enable_accounting;

  };

  static void blk_stat_init(struct blk_rq_stat *stat)
  {
  	stat->min = -1ULL;
  	stat->max = stat->nr_samples = stat->mean = 0;
  	stat->batch = stat->nr_batch = 0;
  }

  static void blk_stat_flush_batch(struct blk_rq_stat *stat)
  {
  	const s32 nr_batch = READ_ONCE(stat->nr_batch);

  	const s32 nr_samples = READ_ONCE(stat->nr_samples);

  
  	if (!nr_batch)
  		return;
  	if (!nr_samples)
  		stat->mean = div64_s64(stat->batch, nr_batch);
  	else {
  		stat->mean = div64_s64((stat->mean * nr_samples) +
  					stat->batch,
  					nr_batch + nr_samples);
  	}
  
  	stat->nr_samples += nr_batch;
  	stat->nr_batch = stat->batch = 0;
  }
  
  static void blk_stat_sum(struct blk_rq_stat *dst, struct blk_rq_stat *src)
  {

  	blk_stat_flush_batch(src);

  	if (!src->nr_samples)
  		return;

  	dst->min = min(dst->min, src->min);
  	dst->max = max(dst->max, src->max);
  
  	if (!dst->nr_samples)
  		dst->mean = src->mean;
  	else {
  		dst->mean = div64_s64((src->mean * src->nr_samples) +
  					(dst->mean * dst->nr_samples),
  					dst->nr_samples + src->nr_samples);
  	}
  	dst->nr_samples += src->nr_samples;
  }

  static void __blk_stat_add(struct blk_rq_stat *stat, u64 value)

  {

  	stat->min = min(stat->min, value);
  	stat->max = max(stat->max, value);

  	if (stat->batch + value < stat->batch ||
  	    stat->nr_batch + 1 == BLK_RQ_STAT_BATCH)
  		blk_stat_flush_batch(stat);

  	stat->batch += value;
  	stat->nr_batch++;

  }

  void blk_stat_add(struct request *rq)

  {

  	struct request_queue *q = rq->q;
  	struct blk_stat_callback *cb;
  	struct blk_rq_stat *stat;
  	int bucket;
  	s64 now, value;
  
  	now = __blk_stat_time(ktime_to_ns(ktime_get()));
  	if (now < blk_stat_time(&rq->issue_stat))
  		return;
  
  	value = now - blk_stat_time(&rq->issue_stat);

  	blk_throtl_stat_add(rq, value);

  	rcu_read_lock();
  	list_for_each_entry_rcu(cb, &q->stats->callbacks, list) {

  		if (!blk_stat_is_active(cb))
  			continue;
  
  		bucket = cb->bucket_fn(rq);
  		if (bucket < 0)
  			continue;
  
  		stat = &get_cpu_ptr(cb->cpu_stat)[bucket];
  		__blk_stat_add(stat, value);
  		put_cpu_ptr(cb->cpu_stat);

  	}

  	rcu_read_unlock();

  }

  static void blk_stat_timer_fn(unsigned long data)

  {

  	struct blk_stat_callback *cb = (void *)data;
  	unsigned int bucket;
  	int cpu;

  	for (bucket = 0; bucket < cb->buckets; bucket++)
  		blk_stat_init(&cb->stat[bucket]);

  	for_each_online_cpu(cpu) {
  		struct blk_rq_stat *cpu_stat;

  		cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu);
  		for (bucket = 0; bucket < cb->buckets; bucket++) {
  			blk_stat_sum(&cb->stat[bucket], &cpu_stat[bucket]);
  			blk_stat_init(&cpu_stat[bucket]);

  		}

  	}

  	cb->timer_fn(cb);

  }

  struct blk_stat_callback *
  blk_stat_alloc_callback(void (*timer_fn)(struct blk_stat_callback *),

  			int (*bucket_fn)(const struct request *),

  			unsigned int buckets, void *data)

  {

  	struct blk_stat_callback *cb;

  	cb = kmalloc(sizeof(*cb), GFP_KERNEL);
  	if (!cb)
  		return NULL;

  	cb->stat = kmalloc_array(buckets, sizeof(struct blk_rq_stat),
  				 GFP_KERNEL);
  	if (!cb->stat) {
  		kfree(cb);
  		return NULL;
  	}
  	cb->cpu_stat = __alloc_percpu(buckets * sizeof(struct blk_rq_stat),
  				      __alignof__(struct blk_rq_stat));
  	if (!cb->cpu_stat) {
  		kfree(cb->stat);
  		kfree(cb);
  		return NULL;
  	}

  	cb->timer_fn = timer_fn;
  	cb->bucket_fn = bucket_fn;
  	cb->data = data;
  	cb->buckets = buckets;
  	setup_timer(&cb->timer, blk_stat_timer_fn, (unsigned long)cb);
  
  	return cb;

  }

  EXPORT_SYMBOL_GPL(blk_stat_alloc_callback);

  void blk_stat_add_callback(struct request_queue *q,
  			   struct blk_stat_callback *cb)

  {

  	unsigned int bucket;
  	int cpu;

  	for_each_possible_cpu(cpu) {
  		struct blk_rq_stat *cpu_stat;

  		cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu);
  		for (bucket = 0; bucket < cb->buckets; bucket++)
  			blk_stat_init(&cpu_stat[bucket]);
  	}

  	spin_lock(&q->stats->lock);
  	list_add_tail_rcu(&cb->list, &q->stats->callbacks);
  	set_bit(QUEUE_FLAG_STATS, &q->queue_flags);
  	spin_unlock(&q->stats->lock);
  }
  EXPORT_SYMBOL_GPL(blk_stat_add_callback);

  void blk_stat_remove_callback(struct request_queue *q,
  			      struct blk_stat_callback *cb)
  {
  	spin_lock(&q->stats->lock);
  	list_del_rcu(&cb->list);

  	if (list_empty(&q->stats->callbacks) && !q->stats->enable_accounting)

  		clear_bit(QUEUE_FLAG_STATS, &q->queue_flags);
  	spin_unlock(&q->stats->lock);

  	del_timer_sync(&cb->timer);

  }

  EXPORT_SYMBOL_GPL(blk_stat_remove_callback);

  static void blk_stat_free_callback_rcu(struct rcu_head *head)

  {

  	struct blk_stat_callback *cb;
  
  	cb = container_of(head, struct blk_stat_callback, rcu);
  	free_percpu(cb->cpu_stat);
  	kfree(cb->stat);
  	kfree(cb);

  }

  void blk_stat_free_callback(struct blk_stat_callback *cb)

  {

  	if (cb)
  		call_rcu(&cb->rcu, blk_stat_free_callback_rcu);

  }

  EXPORT_SYMBOL_GPL(blk_stat_free_callback);

  void blk_stat_enable_accounting(struct request_queue *q)
  {
  	spin_lock(&q->stats->lock);
  	q->stats->enable_accounting = true;
  	set_bit(QUEUE_FLAG_STATS, &q->queue_flags);
  	spin_unlock(&q->stats->lock);
  }

  struct blk_queue_stats *blk_alloc_queue_stats(void)

  {

  	struct blk_queue_stats *stats;
  
  	stats = kmalloc(sizeof(*stats), GFP_KERNEL);
  	if (!stats)
  		return NULL;
  
  	INIT_LIST_HEAD(&stats->callbacks);
  	spin_lock_init(&stats->lock);

  	stats->enable_accounting = false;

  
  	return stats;
  }
  
  void blk_free_queue_stats(struct blk_queue_stats *stats)
  {
  	if (!stats)
  		return;
  
  	WARN_ON(!list_empty(&stats->callbacks));

  	kfree(stats);

  }