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

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

On 08/20/13 17:34, Sagi Grimberg wrote:
> On 8/20/2013 3:50 PM, Bart Van Assche wrote:
>> Certain storage configurations, e.g. a sufficiently large array of
>> hard disks in a RAID configuration, need a queue depth above 64 to
>> achieve optimal performance. Hence make the queue depth configurable.
>> [ ... ]
>
> I noticed this patch in your github and played with it, I agree that
> this patch is needed for a long time...
>
> Question,
> If srp now will allow larger queues while using a single global FMR pool
> of size 1024, isn't it more likely now that in stress environment srp
> will run out of FMRs to handle IO commands?
> I mean that let's say that you have x scsi hosts with can_queue size of
> 512 (+-) and all of them are running IO stress, is it possible that all
> FMRs will be inuse and no FMR is available to register the next IO SG-list?
> Did you try out such a scenario?
>
> I guess that in such a case IB core will return EAGAIN and SRP will
> return SCSI_MLQUEUE_HOST_BUSY.
> I think it is a good Idea to move FMR pools to be per connection rather
> than a global pool, what do you think?

That makes sense to me. And as long as the above has not yet been 
implemented I'm fine with dropping patch 8/8 from this patch set.

Bart.
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