linux-kernel - RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue and CPU queue

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Message-ID: <CY4PR21MB074110983075A3BC91D73AE4CEBA0@CY4PR21MB0741.namprd21.prod.outlook.com>
Date:   Fri, 6 Sep 2019 03:34:42 +0000
From:   Long Li <longli@...rosoft.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
        "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
        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@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue and
 CPU queue

>Subject: RE: [Patch v3] storvsc: setup 1:1 mapping between hardware queue
>and CPU queue
>
>From: Long Li <longli@...rosoft.com> Sent: Thursday, September 5, 2019 3:55
>PM
>>
>> 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 advertises num_present_cpus() as number of hardware queues.
>> This will have upper layer setup 1:1 mapping between hardware queue
>> and CPU queue and avoid unnecessary locking when issuing I/O.
>>
>> Changes:
>> v2: rely on default upper layer function to map queues. (suggested by
>> Ming Lei
>> <tom.leiming@...il.com>)
>> v3: use num_present_cpus() instead of num_online_cpus(). Hyper-v
>> doesn't support hot-add CPUs. (suggested by Michael Kelley
>> <mikelley@...rosoft.com>)
>
>I've mostly seen the "Changes:" section placed below the "---" so that it
>doesn't clutter up the commit log.  But maybe there's not a strong
>requirement one way or the other as I didn't find anything called out in the
>"Documentation/process"
>directory.

Should I resubmit the patch (but keep it v3)?

>
>Michael
>
>>
>> Signed-off-by: Long Li <longli@...rosoft.com>
>> ---
>>  drivers/scsi/storvsc_drv.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
>> index b89269120a2d..cf987712041a 100644
>> --- a/drivers/scsi/storvsc_drv.c
>> +++ b/drivers/scsi/storvsc_drv.c
>> @@ -1836,8 +1836,7 @@ static int storvsc_probe(struct hv_device *device,
>>  	/*
>>  	 * Set the number of HW queues we are supporting.
>>  	 */
>> -	if (stor_device->num_sc != 0)
>> -		host->nr_hw_queues = stor_device->num_sc + 1;
>> +	host->nr_hw_queues = num_present_cpus();
>>
>>  	/*
>>  	 * Set the error handler work queue.
>> --
>> 2.17.1