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Re: [Discuss-gnuradio] Google Summer of Code 2014 applicant : Optimizati

From: West, Nathan
Subject: Re: [Discuss-gnuradio] Google Summer of Code 2014 applicant : Optimization with VOLK
Date: Tue, 25 Feb 2014 17:33:37 -0600

On Tue, Feb 25, 2014 at 4:37 PM, West, Nathan
<address@hidden> wrote:
>>  > On Sun, 2/23/14, Abhishek Bhowmick <address@hidden>
>>  wrote:
>>  >
>>  >  Subject: [Discuss-gnuradio] Google Summer of Code
>>  2014 applicant : Optimization with VOLK
>>  >  To: address@hidden
>>  >  Date: Sunday, February 23, 2014, 8:52 AM
>>  >
>>  >  Hello,
>>  >  I have completed a Bachelor's degree in
>>  >  Electrical Engineering from IIT Bombay, India and
>>  will be
>>  >  joining a masters program in Computer Science in
>>  August. For
>>  >  the summer, I am interested in participating GSoC
>>  2014 and
>>  >  GNU Radio is an organization wheAbhishekre my background
>>  fits
>>  >  nicely.
>>  >
>>  >>  > --------------------------------------------
>>  >  I went through the ideas page and was
>>  >  particularly interested in doing performance
>>  optimization
>>  >  with VOLK. After going through some online
>>  documentation
>>  >  about the library and the SDR'12 paper, I
>>  realised that
>>  >  following areas need work :
>>  >
>>  >  1. Profiling GNU radio code to identify new
>>  >  kernels and implement them for existing Intel
>>  SIMD
>>  >  extensions, also porting kernels to other ISA
>>  extensions.
>>  >  2. Better testing of the effects of more complex
>>  >  scheduler logic on larger environments (beyond
>>  simple
>>  >  kernels)
>>  >
>>  >  3. Exploring extension of Volk to GPU ISAs, to
>>  >  leverage chips such as AMD Fusion (However, this
>>  seems to
>>  >  more research than software development)
>>  >
>>  >  According to the GSoC proposal, point (1) seems
>>  >  to be the expectation. Given this, I would like
>>  some advice
>>  >  on how to go ahead looking for potential ideas
>>  (and some
>>  >  feedback on feasibility of the other ideas as
>>  well)
>>  >
>>  >
>>  >  My background : C++, Python, Signal Processing,
>>  >  Computer Architecture
>>  >
>>  >  Thanks,
>>  >  Abhishek Bhowmick
>>  >
> This is a great conversation, and I'll take the opportunity to plug
> the up coming VOLK working group call
> (https://plus.google.com/u/1/events/ch3jrjcvp7mdiqelpismfieg3n0).
> Bogdan, your results aren't particula>  >
> --------------------------------------------
> rly surprising, but the feedback is really good to hear.
> Back to GSoC:
> Abhishek,
>>Thanks for the pointers to gr-atsc and gr-80211. I have started
>>looking there as a
>>starting point. Are there similar modules which are undergoing volk
>>speedup fixes?
>>I am also trying to meet up with other people who have been using GNU radio
>>to identify potential modules for acceleration. As you are now a
>>mentor organization, I feel it's a good time for us to get into
>>detailed discussions.
> From the previous discussion it should be apparent that how algorithms
> are implemented will make the biggest difference, and that the new
> acceleration is primarily going to come from larger more complex
> kernels. At the end of the day it's going to be your proposal. So far
> on the list of places to look we have
> * in-tree OFDM (contact Martin)
> * gr-atsc (use Andrew Davis' fork)
> * gr-dvbt
> * gr-fecapi
> For your proposal I would recommend looking at their code, then
> getting in contact with the author(s) of those modules to ask about
> their thoughts on accelerating blocks they have written. The reality
> of this project is that we are accelerating some signal processing
> algorithm and knowledge of that algorithm is useful for acceleration.
> Whatever application you have interested and/or knowledge in (fresh
> out of a BS it's more likely to be interest) should guide your
> proposal. If you know anything about error correcting codes then the
> latter 2 would be good fits. OFDM frame detection probably has a
> gentler learning curve since at the basic level you're looking at
> convolution, and there's papers you can look for on more involved
> algorithms. Other algorithms to look at might include agc or
> equalizers.
> If you're interested in GPU programming don't forget to checkout gr-gpu.
>>> At the moment the only mainstream ISA not being targeted is probably
>>> AVX2, which has
>>> some nice features for the type of kernels we're doing.  If you went
>>> that route it would likely need add
>>> protokernels to a pretty large number of kernels.
>>> Nathan
>>This also seems to be promising, though I guess it would require me to
>>come up to speed with AVX2 (which I would love to do). Could you
>>please elaborate
>>a little on the kind of beneficial features you have in mind ? I am
>>concerned that the
>>job of adding proto-kernels might turn out to be mundane/tedious ? Is
>>that a valid concern ?
> Right, so as Martin mentioned the answer is sort of relative. I
> wouldn't go so far as to say it's mundane, especially if you have
> little 
> experienhttp://gnss-sdr.org/documentation/google-summer-code-2014-ideas-listce
>  with using intrinsics and SIMD instructions. One
> reason AVX isn't so prominently featured (I suspect) is that the
> instructions are almost the same as SSE instructions, but the vectors
> are twice as long so that is actually mundane. AVX2/FMA extensions
> introduce some new features to the amd64 instruction set. The most
> obvious being that it looks like Intel and AMD finally settled in on
> the same fused multiply-add (there's also a multiply-subtract that's
> good for complex numbers) implementation. That will likely be able to
> speed things up a bit, but I'm also looking forward to seeing gains
> from the various load_gathers that have been introduced. They allow
> you to do a single load operation that gathers vector elements that
> span pretty large ranges. VOLK won't be so interested in the large
> ranges (except maybe decimators), but it could be useful for loading
> complex vectors. There's some other math functions we may be able to
> leverage, but those are two features that I think would be widely
> applicable.
> In your proposal you should definitely include what ISAs you intend to
> use, and if there are features specific to that instruction set then
> point out why it's a good choice. This is mostly important for
> choosing between SSE and friends, AVX, AVX2/FMA. It would be good to
> see plans that include NEON support for anything you'd add to amd64
> platforms, but that's not a requirement.
> Nathan

I also see that GNSS-SDR made it to GSoC and they have a VOLK related project.

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