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

[Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>]

On 09/13/13 10:06, Jack Wang wrote:
> On 09/12/2013 06:30 PM, Bart Van Assche wrote:
>> On 09/12/13 18:16, Jack Wang wrote:
>>> On 09/12/2013 12:16 AM, David Dillow wrote:
>>>> On Tue, 2013-09-10 at 19:44 +0200, Bart Van Assche wrote:
>>>>> If this name was not yet in use in any interface that is visible in
>>>>> user
>>>>> space, I would agree that we should come up with a better name.
>>>>> However,
>>>>> the SCSI mid-layer already uses that name today to export the queue
>>>>> size. To me this looks like a good reason to use the name "can_queue" ?
>>>>> An example:
>>>>>
>>>>> $ cat /sys/class/scsi_host/host93/can_queue
>>>>> 62
>>>>
>>>> Yes, I know it has been used before, but I'm torn between not furthering
>>>> a bad naming choice and consistency. Foolish consistency and all that...
>>>>
>>>> I really don't like "can_queue", but I'll not complain if Roland decides
>>>> to take it as-is.
>>>
>>> What the allow range for this queue size?
>>> Default cmd_per_lun and can_queue with same value makes no sense to me.
>>> Could we bump can_queue to bigger value like 512?
>>
>> Increasing the default value is only necessary when using a hard disk
>> array at the target side. When using a single hard disk or an SSD at the
>> target side the default value is fine.
>
> Agree, from another side increasing default can_queue value is harmless
> for single harddisk/SSD, but will boot performance for multiple LUN
> attached to same host, so why not?

Increasing that parameter increases memory consumption for each path 
between initiator and target. In a setup where both the initiator and 
the target have multiple IB ports the number of paths can be large even 
when only a single LUN is exported by the target. That's why I'm not 
enthusiast about increasing the default value of the queue size.

Bart.
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