Re: [Discuss-gnuradio] Google Summer of Code 2014 applicant : Optimization with VOLK

[Johannes Demel]

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Hi Florian,

the generic implementation serves 2 purposes, at least in my opinion.
Firstly, in case the necessary hardware extension is not available on
the target hardware, there is a backup default.
Secondly, the generic implementation is usually easier to read and
thus preferable as a reference. I know that this is a 'the code is the
documentation' argument. But even though documentation might be really
good, sometimes looking at the code just makes things clearer.

happy hacking
Johannes

On 11.03.2014 23:08, Florian Kaltenberger wrote:
> Hi Nathan and Abhishek,
> 
> On 10/03/2014 23:22, West, Nathan wrote:
>> Ah! So there was a slight miscommunication. Yes, porting the
>> OpenAirInterfaces SIMD code to VOLK is a good option as well. The
>> turbo channel coder/decoder is part of that. I've *briefly*
>> looked at the code to see what is currently there, and it's my
>> understanding that the work involved will be to write generic C
>> implementations of vectorized code where the generic version does
>> not exist. Beyond that porting to newer/different ISAs (AVX or
>> NEON depending on your preference and hardware availability). I
>> think Florian is on the gr-discuss mailing list, but I've CCed
>> him to hopefully provide more details as he's more familiar with
>> the original code base.
> I only joined this mailing list recently, so I probably missed a
> part of the discussion. Let me summarize briefly what
> OpenAirInterface can provide. We have optimized SIMD (SSE4)
> implementations of the LTE turbo encoder and decoder as well as the
> LTE tail-biting Viterbi encoder and decoder. We also have the
> 802.11 Viterbi encoder and decoder. The only functions for which we
> have generic non-vectorized functional equivalents is the LTE turbo
> decoder. I am not sure I understand why it is necessary to write
> generic versions for the already optimized SIMD code. My idea was
> to port the optimized SIMD code from OpenAirInterface to VOLK, such
> that is can be used by GR applications. I am not familiar with VOLK
> (yet) but this might just be as easy as writing a wrapper
> function. As Nathan suggested, the more interesting part is
> probably to upgrade the code to AVX2 or similar.
> 
> Cheers, Florian.
> 
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