Spread queues among present CPUs first, then building the 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 this unbalanced mapping between CPUs and queues. The similar policy has been applied on Managed IRQ affinity. Reported-by: Yi Zhang <[email protected]> Cc: Yi Zhang <[email protected]> Signed-off-by: Ming Lei <[email protected]> --- block/blk-mq-cpumap.c | 34 +++++++++++++++++++++++----------- 1 file changed, 23 insertions(+), 11 deletions(-) diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c index f945621a0e8f..e217f3404dc7 100644 --- a/block/blk-mq-cpumap.c +++ b/block/blk-mq-cpumap.c @@ -15,10 +15,9 @@ #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, const int q) { - return qmap->queue_offset + (cpu % nr_queues); + return qmap->queue_offset + q; } static int get_first_sibling(unsigned int cpu) @@ -36,23 +35,36 @@ 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, 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); + first_sibling = get_first_sibling(cpu); + if (first_sibling == cpu) { + map[cpu] = queue_index(qmap, q); + q = (q + 1) % nr_queues; } else { - first_sibling = get_first_sibling(cpu); - if (first_sibling == cpu) - map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu); - else - map[cpu] = map[first_sibling]; + map[cpu] = map[first_sibling]; } } -- 2.20.1
