On 7/25/19 4:26 PM, Ming Lei wrote:
> 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 <yi.zhang@xxxxxxxxxx>
> Cc: Yi Zhang <yi.zhang@xxxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> 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);
Why not keep this similarly?
> + 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];
Then no need to share queue if nr_queues is enough for all possible cpu.
Regards, -Bob
