Commit 556f36e9 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: balance mapping between present CPUs and queues 



Spread queues among present CPUs first, then building mapping on other
non-present CPUs.

So we can minimize count of dead queues which are mapped by un-present
CPUs only. Then bad IO performance can be avoided by unbalanced mapping
between present CPUs and queues.

The similar policy has been applied on Managed IRQ affinity.

Cc: Yi Zhang <yi.zhang@redhat.com>
Reported-by: default avatarYi Zhang <yi.zhang@redhat.com>
Reviewed-by: default avatarBob Liu <bob.liu@oracle.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b7e9e1fb

block/blk-mq-cpumap.c

+22 −7
Original line number Diff line number Diff line
@@ -15,10 +15,10 @@ 
#include "blk.h"

#include "blk-mq.h"



static int cpu_to_queue_index(struct blk_mq_queue_map *qmap,

			      unsigned int nr_queues, const int cpu)

static int queue_index(struct blk_mq_queue_map *qmap,

		       unsigned int nr_queues, const int q)

{

	return qmap->queue_offset + (cpu % nr_queues);

	return qmap->queue_offset + (q % nr_queues);

}



static int get_first_sibling(unsigned int cpu)
@@ -36,21 +36,36 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap) 
{

	unsigned int *map = qmap->mq_map;

	unsigned int nr_queues = qmap->nr_queues;

	unsigned int cpu, first_sibling;

	unsigned int cpu, first_sibling, q = 0;



	for_each_possible_cpu(cpu)

		map[cpu] = -1;



	/*

	 * Spread queues among present CPUs first for minimizing

	 * count of dead queues which are mapped by all un-present CPUs

	 */

	for_each_present_cpu(cpu) {

		if (q >= nr_queues)

			break;

		map[cpu] = queue_index(qmap, nr_queues, q++);

	}



	for_each_possible_cpu(cpu) {

		if (map[cpu] != -1)

			continue;

		/*

		 * 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 performance optimizations.

		 */

		if (cpu < nr_queues) {

			map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);

		if (q < nr_queues) {

			map[cpu] = queue_index(qmap, nr_queues, q++);

		} else {

			first_sibling = get_first_sibling(cpu);

			if (first_sibling == cpu)

				map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);

				map[cpu] = queue_index(qmap, nr_queues, q++);

			else

				map[cpu] = map[first_sibling];

		}

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