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

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Message-ID: <CY4PR21MB07415687EE2329FF320A152ECEA50@CY4PR21MB0741.namprd21.prod.outlook.com>
Date:   Thu, 22 Aug 2019 19:31:47 +0000
From:   Long Li <longli@...rosoft.com>
To:     Ming Lei <tom.leiming@...il.com>,
        "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>
CC:     KY 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-hyperv@...r.kernel.org>,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] storvsc: setup 1:1 mapping between hardware queue and CPU
 queue

>>>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 for the pointer. I'm sending a v2.

Long

>>>
>>>thanks,
>>>Ming Lei