Re: [PATCH 8/8] IB/srp: Make queue size configurable

[Jack Wang <xjtuwjp-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 09/13/2013 04:15 PM, Jack Wang wrote:
> On 09/13/2013 04:03 PM, Bart Van Assche wrote:
>> On 09/13/13 15:51, Jack Wang wrote:
>>> On 09/13/2013 03:33 PM, Bart Van Assche wrote:
>>>> On 09/13/13 14:25, Jack Wang wrote:
>>>>> I tried your srp-ha branch in github,
>>>>> echo string
>>>>>> SRP2="id_ext=${THCA2_GUID},ioc_guid=${THCA2_GUID},dgid=${TGID_P2},pkey=${PKEY},service_id=${THCA2_GUID},can_queue=512"
>>>>>>
>>>>>>
>>>>> to add_target failed with
>>>>>
>>>>>>    ib_srp: unknown parameter or missing value 'can_queue=512
>>>>>> [  122.405385] ' in target creation request
>>>>> Do I miss something?
>>>>
>>>> Hello Jack,
>>>>
>>>> Have you already tried the same command with "echo -n" instead of "echo"
>>>> ? If I remember correctly the SRP initiator doesn't like a newline at
>>>> the end of the string written into the sysfs add_target attribute.
>>>>
>>>> Hope this helps,
>>>>
>>>> Bart.
>>>>
>>> Thanks Bart,
>>>
>>> You're right, that is the problem, with -n option I can set can_queue
>>> successfully.
>>>
>>> But cat /sys/class/scsi_host/hostx/can_queue still show 63
>>>
>>> Looks like it cause by the logic below:
>>>
>>>
>>>>     /*
>>>> 1870                  * Reserve credits for task management so we don't
>>>> 1871                  * bounce requests back to the SCSI mid-layer.
>>>> 1872                  */
>>>> 1873                 target->scsi_host->can_queue
>>>> 1874                         = min(target->req_lim -
>>>> SRP_TSK_MGMT_SQ_SIZE,
>>>> 1875                               target->scsi_host->can_queue);
>>>> 1876                 target->scsi_host->cmd_per_lun
>>>> 1877                         = min_t(int, target->scsi_host->can_queue,
>>>> 1878                                 target->scsi_host->cmd_per_lun);
>>>
>>> Could you give some hint on this, why we need to update can_queue and
>>> cmd_per_lun here?
>>
>> Hello Jack,
>>
>> What is the value of target->req_lim on your setup ? The initiator
>> limits the queue size to the target request limit because any attempt to
>> queue more commands would cause the target to reply with "BUSY" anyway.
>>
>> Bart.
>>
>>
> Hello Bart,
> 
>> cat /sys/class/scsi_host/host36/req_lim 
>> 64
> 
> I just checked srp spec, which do define such behaviour, I wonder in
> SCST/SRPT, how the request limit is chosen, is it report from low level
> hardware driver?
> 
> Thanks
> Jack
> 
> 
> 

Reply to myself. SRPT default use in login_rsp request limit.
> #define SCST_MAX_TGT_DEV_COMMANDS            64

Cheers,
Jack

The
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