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blk-mq: balance mapping between present CPUs and queues

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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: Yi Zhang <yi.zhang@redhat.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2019-07-25 17:41:46 +08:00 committed by Jens Axboe
parent b7e9e1fb7a
commit 556f36e90d
1 changed files with 22 additions and 7 deletions
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29
block/blk-mq-cpumap.c
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@ -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];
}