Re: [Discuss-gnuradio] Speed Optimization and Application for ATSC Receivers

[Martin Braun]

Josh,

great to see you getting interested and being so proactive about getting
started!

Cheers,
Martin

On 03/06/2016 08:37 PM, Joshua Lilly wrote:
> Andy and Nathan,
> I really appreciate the insight, resources and the direction you have
> provided. I am starting to look into adding the constants to the blocks.
> When I run into questions, I will check in on irc or send another email.
> 
> Thanks again for all of the help!
> 
> Josh
> 
> On Mar 06, 2016, at 01:08 PM, Andy Walls <address@hidden>
> wrote:
> 
>> On Sun, 2016-03-06 at 08:49 -0500, address@hidden
>> <mailto:address@hidden>
>> wrote:
>>> Message: 5
>>> Date: Sun, 06 Mar 2016 06:45:13 +0000 (GMT)
>>> From: Joshua Lilly
>>
>>
>>> Hello,
>>> My name is Josh and I am interested in getting involved in GNU radio.
>>> Specifically, I would like to work on the above project idea for
>>> google summer of code 2016 by implementing Viterbi and demux
>>> algorithms in volk and testing the speed improvements. I have
>>> experience with python, c/c++, boost, and profiling with valgrind. I
>>> currently have read the getting involved page, compiled the code, I am
>>> working my way through some of the tutorials, and I have read through
>>> the code in volk. Even if I don't get accepted to google summer of
>>> code, I would still like to get involved in fixing bugs, or something
>>> since this seems like a really awesome project.
>>
>> Hi Josh:
>>
>> I'm only a kibitzer when it comes to the project, so I can't say
>> anything about GSoC acceptance.
>>
>>
>>> If it isn't too much to ask could someone point me to a nice beginner
>>> bug to fix in order to get my hands in the code?
>>
>> However I can give you (and anyone who wants it) a relevant beginner
>> +intermediate thing to get your hands in the code. The "intermediate"
>> part comes from your request to play in volk, which I don't consider
>> stuff for beginners.
>>
>> So we'll start with a very conceptually simple thing to improve: adding
>> constant(s) to a sample stream. Specifically measuring and improving
>> the performance of the add_const_vXX and add_const_XX blocks in
>> gnuradio/gr-blocks/lib.
>>
>> See the attached GRC flowgraph and hand-tweaked add_const_performance.py
>> python script.
>>
>>
>> 1. Measure the baseline performance of both the add_const_vss and
>> add_const_ss blocks at the high sample rate of 160 Msps.
>>
>> $ ps -eLo pcpu,pid,tid,cls,rtprio,pcpu,comm
>>
>> shows the add_const_vss or add_const_ss thread hovering around 70% and
>> 57% repsectively.
>>
>> For meaningful measurements you must run the flowgraph RT prioirty.
>>
>>
>> 2. For an immediate performance increase for most users, add a new
>> gnuradio/gr-blocks/grc/blocks_add_const_xx.xml to the build that allows
>> users to select the faster, non-vector version of the add const block
>> from the GUI.
>>
>>
>> 3. Measure the baseline of where the most CPU is being consumed in these
>> blocks.
>> You can use perf tools or oprofile tools or whatever works for you.
>> For meaningful measurements you must run the flowgraph RT priority.
>> Odds are, it's the block's work() function that is consuming most of the
>> CPU.
>>
>>
>> 4. Create volk kernels to replace the main operations in the work()
>> functions of these blocks, if you can. Since adding a constant is so
>> simple, and ORC is very good about optimizing simple things, the volk
>> implementations should include an ORC implementation if possible. Odds
>> are the ORC implementation will beat hand-written SIMD versions for x86
>> processors. Use volk_profile to prove my guess about ORC right or
>> wrong. :)
>>
>>
>> 5. Create volk-ized versions of the add_const blocks and remeasure their
>> performance. How much improvement did you get?
>>
>>
>> 6. Don't forget to add QA tests for the new volk functions.
>>
>>
>> As an alternate to the above:
>>
>> 1. Improve the performance of the nlog10_ff block by using log2,
>> algebra, volk, and skipping the add of k at the end, if k == 0.0.
>>
>> 2. Create a new approx_nlog10_ff block by taking advantage of the fact
>> that the log2 exponent in IEEE floats can be obtained with a mask and
>> shift operation. Don't forget to add a GRC .xml file for the block and
>> QA test code.
>>
>>> Thank you,
>>> Josh
>>
>>
>> Regards,
>> Andy
> 
> 
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