linux/block/blk-mq-cpumap.c
Bart Van Assche 959f5f5b2f blk-mq: Use all available hardware queues
Suppose that a system has two CPU sockets, three cores per socket,
that it does not support hyperthreading and that four hardware
queues are provided by a block driver. With the current algorithm
this will lead to the following assignment of CPU cores to hardware
queues:

  HWQ 0: 0 1
  HWQ 1: 2 3
  HWQ 2: 4 5
  HWQ 3: (none)

This patch changes the queue assignment into:

  HWQ 0: 0 1
  HWQ 1: 2
  HWQ 2: 3 4
  HWQ 3: 5

In other words, this patch has the following three effects:
- All four hardware queues are used instead of only three.
- CPU cores are spread more evenly over hardware queues. For the
  above example the range of the number of CPU cores associated
  with a single HWQ is reduced from [0..2] to [1..2].
- If the number of HWQ's is a multiple of the number of CPU sockets
  it is now guaranteed that all CPU cores associated with a single
  HWQ reside on the same CPU socket.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-12-09 09:08:21 -07:00

120 lines
2.5 KiB
C

/*
* 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_cpus, unsigned int nr_queues,
const int cpu)
{
return cpu * nr_queues / nr_cpus;
}
static int get_first_sibling(unsigned int cpu)
{
unsigned int ret;
ret = cpumask_first(topology_thread_cpumask(cpu));
if (ret < nr_cpu_ids)
return ret;
return cpu;
}
int blk_mq_update_queue_map(unsigned int *map, unsigned int nr_queues)
{
unsigned int i, nr_cpus, nr_uniq_cpus, queue, first_sibling;
cpumask_var_t cpus;
if (!alloc_cpumask_var(&cpus, GFP_ATOMIC))
return 1;
cpumask_clear(cpus);
nr_cpus = nr_uniq_cpus = 0;
for_each_online_cpu(i) {
nr_cpus++;
first_sibling = get_first_sibling(i);
if (!cpumask_test_cpu(first_sibling, cpus))
nr_uniq_cpus++;
cpumask_set_cpu(i, cpus);
}
queue = 0;
for_each_possible_cpu(i) {
if (!cpu_online(i)) {
map[i] = 0;
continue;
}
/*
* Easy case - we have equal or more hardware queues. Or
* there are no thread siblings to take into account. Do
* 1:1 if enough, or sequential mapping if less.
*/
if (nr_queues >= nr_cpus || nr_cpus == nr_uniq_cpus) {
map[i] = cpu_to_queue_index(nr_cpus, nr_queues, queue);
queue++;
continue;
}
/*
* Less then nr_cpus queues, and we have some number of
* threads per cores. Map sibling threads to the same
* queue.
*/
first_sibling = get_first_sibling(i);
if (first_sibling == i) {
map[i] = cpu_to_queue_index(nr_uniq_cpus, nr_queues,
queue);
queue++;
} else
map[i] = map[first_sibling];
}
free_cpumask_var(cpus);
return 0;
}
unsigned int *blk_mq_make_queue_map(struct blk_mq_tag_set *set)
{
unsigned int *map;
/* If cpus are offline, map them to first hctx */
map = kzalloc_node(sizeof(*map) * nr_cpu_ids, GFP_KERNEL,
set->numa_node);
if (!map)
return NULL;
if (!blk_mq_update_queue_map(map, set->nr_hw_queues))
return map;
kfree(map);
return NULL;
}
/*
* 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 cpu_to_node(i);
}
return NUMA_NO_NODE;
}