On Wed, Jun 30, 2021 at 11:51:53AM +0800, Ming Lei wrote:
> The default queue mapping builder of blk_mq_map_queues doesn't take NUMA
> topo into account, so the built mapping is pretty bad, since CPUs
> belonging to different NUMA node are assigned to same queue. It is
> observed that IOPS drops by ~30% when running two jobs on same hctx
> of null_blk from two CPUs belonging to two NUMA nodes compared with
> from same NUMA node.
>
> Address the issue by reusing irq_create_affinity_masks() for building
> the default queue mapping, so that we can re-use the mapping created
> for managed irq.
>
> Lots of drivers may benefit from the change, such as nvme pci poll,
> nvme tcp, ...
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq-cpumap.c | 60 +++++++++----------------------------------
> 1 file changed, 12 insertions(+), 48 deletions(-)
>
> diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
> index 3db84d3197f1..946e373296a3 100644
> --- a/block/blk-mq-cpumap.c
> +++ b/block/blk-mq-cpumap.c
> @@ -10,67 +10,31 @@
> #include <linux/mm.h>
> #include <linux/smp.h>
> #include <linux/cpu.h>
> +#include <linux/interrupt.h>
>
> #include <linux/blk-mq.h>
> #include "blk.h"
> #include "blk-mq.h"
>
> -static int queue_index(struct blk_mq_queue_map *qmap,
> - unsigned int nr_queues, const int q)
> -{
> - return qmap->queue_offset + (q % nr_queues);
> -}
> -
> -static int get_first_sibling(unsigned int cpu)
> -{
> - unsigned int ret;
> -
> - ret = cpumask_first(topology_sibling_cpumask(cpu));
> - if (ret < nr_cpu_ids)
> - return ret;
> -
> - return cpu;
> -}
> -
> int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
> {
> + struct irq_affinity_desc *masks = NULL;
> + struct irq_affinity affd = {0};
> unsigned int *map = qmap->mq_map;
> unsigned int nr_queues = qmap->nr_queues;
> - unsigned int cpu, first_sibling, q = 0;
> + unsigned int q;
>
> - for_each_possible_cpu(cpu)
> - map[cpu] = -1;
> + masks = irq_create_affinity_masks(nr_queues, &affd);
> + if (!masks)
> + return -ENOMEM;
>
> - /*
> - * 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 (q = 0; q < nr_queues; q++) {
> + unsigned int cpu;
>
> - 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 (q < nr_queues) {
> - map[cpu] = queue_index(qmap, nr_queues, q++);
> - } else {
> - first_sibling = get_first_sibling(cpu);
> - if (first_sibling == cpu)
> - map[cpu] = queue_index(qmap, nr_queues, q++);
> - else
> - map[cpu] = map[first_sibling];
> - }
> + for_each_cpu(cpu, &masks[q].mask)
> + map[cpu] = q;
oops, the above line should have been:
map[cpu] = qmap->queue_offset + q;
Thanks,
Ming
