linux-kernel - Re: [PATCH v2 01/17] ibmvfc: add vhost fields and defaults for MQ enablement

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Message-ID: <38903a4f-9253-0b4b-6f67-af78ec86175f@linux.ibm.com>
Date:   Wed, 2 Dec 2020 09:27:11 -0800
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     Brian King <brking@...ux.vnet.ibm.com>,
        james.bottomley@...senpartnership.com
Cc:     martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        brking@...ux.ibm.com
Subject: Re: [PATCH v2 01/17] ibmvfc: add vhost fields and defaults for MQ
 enablement

On 12/2/20 7:14 AM, Brian King wrote:
> On 12/1/20 6:53 PM, Tyrel Datwyler wrote:
>> Introduce several new vhost fields for managing MQ state of the adapter
>> as well as initial defaults for MQ enablement.
>>
>> Signed-off-by: Tyrel Datwyler <tyreld@...ux.ibm.com>
>> ---
>>  drivers/scsi/ibmvscsi/ibmvfc.c |  9 ++++++++-
>>  drivers/scsi/ibmvscsi/ibmvfc.h | 13 +++++++++++--
>>  2 files changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
>> index 42e4d35e0d35..f1d677a7423d 100644
>> --- a/drivers/scsi/ibmvscsi/ibmvfc.c
>> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c
>> @@ -5161,12 +5161,13 @@ static int ibmvfc_probe(struct vio_dev *vdev, const struct vio_device_id *id)
>>  	}
>>  
>>  	shost->transportt = ibmvfc_transport_template;
>> -	shost->can_queue = max_requests;
>> +	shost->can_queue = (max_requests / IBMVFC_SCSI_HW_QUEUES);
> 
> This doesn't look right. can_queue is the SCSI host queue depth, not the MQ queue depth.

Our max_requests is the total number commands allowed across all queues. From
what I understand is can_queue is the total number of commands in flight allowed
for each hw queue.

        /*
         * In scsi-mq mode, the number of hardware queues supported by the LLD.
         *
         * Note: it is assumed that each hardware queue has a queue depth of
         * can_queue. In other words, the total queue depth per host
         * is nr_hw_queues * can_queue. However, for when host_tagset is set,
         * the total queue depth is can_queue.
         */

We currently don't use the host wide shared tagset.

-Tyrel

> 
>>  	shost->max_lun = max_lun;
>>  	shost->max_id = max_targets;
>>  	shost->max_sectors = IBMVFC_MAX_SECTORS;
>>  	shost->max_cmd_len = IBMVFC_MAX_CDB_LEN;
>>  	shost->unique_id = shost->host_no;
>> +	shost->nr_hw_queues = IBMVFC_SCSI_HW_QUEUES;
>>  
>>  	vhost = shost_priv(shost);
>>  	INIT_LIST_HEAD(&vhost->sent);
> 
> 
>