Re: [Discuss-gnuradio] Try to improve E100's performance at high sample rate

[ziyang]

> I dont recommend using the extra blocks, that would probably cause more
> overhead. Looking at gr_quadrature_demod_cf::work, it looks like you can
> vectorize the operation of the conjugate multiply, then the atan, then
> the gain scaler. So, that would be one for loop that operates on 4
> samples at a time, and calls 3 volk functions.

Hi, Josh. I implemented a quadrature_demod_cf block (please find it in 
the attachment). Since the Volk atan2 function is currently only for SSE 
as Nick said, and there is no conjugate-multiply function for FC32 
inputs, I use Gnuradio's built-in conjugate and fast_atan_2f functions, 
plus two volk multiply functions. The for loop is timed by 
high_res_timer. Besides, the work function of gr_quadrature_demod_cf is 
timed for comparison purpose (also attached). Each of these two blocks 
is connected to a file_source which provides modulated data.

I tested two blocks individually, firstly on a PC with Intel processor, 
then on E100. On PC, it always take volk-based block less time to 
demodulate a same-size-buffer of data (i.e. for 4096 input items, it 
takes the original quadrature_demod_cf block 0.185 ms but takes 
volk-based block only 0.163 ms to demodulate).

However, the results are different on E100: sometimes the original block 
runs faster, sometimes the volk-based block does. I ran the tests for 
several times, although the recorded time changes by some tens 
(occasionally a few handreds) of nanoseconds, but neither block is 
always faster than the other.

Now I'm confused by the results, since I expected the volk-ified 
demodulator to be faster. Could you give me some help on this issue? Thanks.


Best Regards,

Terry

volk_quad_demod_workfunc.cc
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gr_quadrature_demod_cf_workfunc.cc
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