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

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Date:   Thu, 22 Aug 2019 18:55:32 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     longli@...uxonhyperv.com
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-hyperv@...r.kernel.org,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Long Li <longli@...rosoft.com>
Subject: Re: [PATCH] storvsc: setup 1:1 mapping between hardware queue and CPU queue

On Tue, Aug 20, 2019 at 3:36 AM <longli@...uxonhyperv.com> wrote:
>
> From: Long Li <longli@...rosoft.com>
>
> 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@...rosoft.com>
> ---
>  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