Re: [PATCH] storvsc: setup 1:1 mapping between hardware queue and CPU queue

[Ming Lei]

On Tue, Aug 20, 2019 at 3:36 AM <longli@xxxxxxxxxxxxxxxxx> wrote:
>
> From: Long Li <longli@xxxxxxxxxxxxx>
>
> storvsc doesn't use a dedicated hardware queue for a given CPU queue. When
> issuing I/O, it selects returning CPU (hardware queue) dynamically based on
> vmbus channel usage across all channels.
>
> This patch sets up a 1:1 mapping between hardware queue and CPU queue, thus
> avoiding unnecessary locking at upper layer when issuing I/O.
>
> Signed-off-by: Long Li <longli@xxxxxxxxxxxxx>
> ---
>  drivers/scsi/storvsc_drv.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index b89269120a2d..26c16d40ec46 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1682,6 +1682,18 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
>         return 0;
>  }
>
> +static int storvsc_map_queues(struct Scsi_Host *shost)
> +{
> +       unsigned int cpu;
> +       struct blk_mq_queue_map *qmap = &shost->tag_set.map[HCTX_TYPE_DEFAULT];
> +
> +       for_each_possible_cpu(cpu) {
> +               qmap->mq_map[cpu] = cpu;
> +       }

Block layer provides the helper of blk_mq_map_queues(), so suggest you to use
the default cpu mapping, instead of inventing a new one.

thanks,
Ming Lei