/*
   * CPU <-> hardware queue mapping helpers
   *
   * Copyright (C) 2013-2014 Jens Axboe
   */
  #include <linux/kernel.h>
  #include <linux/threads.h>
  #include <linux/module.h>
  #include <linux/mm.h>
  #include <linux/smp.h>
  #include <linux/cpu.h>
  
  #include <linux/blk-mq.h>
  #include "blk.h"
  #include "blk-mq.h"
  
  static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)
  {
  	return cpu % nr_queues;
  }
  
  static int get_first_sibling(unsigned int cpu)
  {
  	unsigned int ret;
  
  	ret = cpumask_first(topology_sibling_cpumask(cpu));
  	if (ret < nr_cpu_ids)
  		return ret;
  
  	return cpu;
  }
  
  int blk_mq_map_queues(struct blk_mq_tag_set *set)
  {
  	unsigned int *map = set->mq_map;
  	unsigned int nr_queues = set->nr_hw_queues;
  	unsigned int cpu, first_sibling;
  
  	for_each_possible_cpu(cpu) {
  		/*
  		 * First do sequential mapping between CPUs and queues.
  		 * In case we still have CPUs to map, and we have some number of
  		 * threads per cores then map sibling threads to the same queue for
  		 * performace optimizations.
  		 */
  		if (cpu < nr_queues) {
  			map[cpu] = cpu_to_queue_index(nr_queues, cpu);
  		} else {
  			first_sibling = get_first_sibling(cpu);
  			if (first_sibling == cpu)
  				map[cpu] = cpu_to_queue_index(nr_queues, cpu);
  			else
  				map[cpu] = map[first_sibling];
  		}
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(blk_mq_map_queues);
  
  /*
   * We have no quick way of doing reverse lookups. This is only used at
   * queue init time, so runtime isn't important.
   */
  int blk_mq_hw_queue_to_node(unsigned int *mq_map, unsigned int index)
  {
  	int i;
  
  	for_each_possible_cpu(i) {
  		if (index == mq_map[i])
  			return local_memory_node(cpu_to_node(i));
  	}
  
  	return NUMA_NO_NODE;
  }