Re: [PATCH for kernel v4.6] IB/srpt: Revert "Convert to percpu_ida tag allocation"

[Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>]

On 03/31/16 20:05, Leon Romanovsky wrote:
> On Thu, Mar 31, 2016 at 05:01:39PM -0700, Bart Van Assche wrote:
>> That patch is wrong because it makes the ib_srpt driver use I/O
>> contexts allocated by transport_alloc_session_tags() but it does
>> not initialize these I/O contexts properly.
>
> Did you have a chance to see which initializations are missing in this
> case? What is needed to do if we decide to fix original patch?
>
> Except these questions, the revert is fine :)
> Reviewed-by: Leon Romanovsky <leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>

Hello Leon,

Thanks for the review. The initializations that are missing from that 
patch are the 'buf' pointer in the srpt_ioctx structure and mapping that 
buffer for DMA. Another bug introduced by that patch is that it doubles 
the amount of memory that is allocated for I/O contexts. New I/O context 
allocations were added by that patch but the existing I/O context 
allocation code was not removed.

Regarding reconsidering the original patch: before we do that it has to 
be shown with numbers that the percpu_ida conversion does not decrease 
performance. This is something I had already asked two months ago. See 
also 
http://thread.gmane.org/gmane.linux.scsi.target.devel/11253/focus=110559.

Bart.
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