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

[Josh Blum]

On 01/16/2012 09:51 AM, ziyang wrote:
> On 01/13/2012 09:30 PM, Josh Blum wrote:
>>> To reduce the computation load of the processor, I tried two methods:
>>> 1) modify the gr.quadrature_demod_cf block, replace some multiplication
>>> operations with volk-based operations (gr.multiply and gr.multiply_const
>>> modules in gr_blocks);
>> I like it. Make sure to contribute patches like that back. :-)
> Actually, what I did was writing a new quadrature_demod block without
> the multiplication and delay operations, and connect extra gr.multiply
> and gr.delay blocks instead in the flow graph. Because my understanding
> is that the volk functions take a vector (multiple values) as input, and
> I didn't figure out a way to do the single-item-operation in the volk
> style.
> 

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.

>> Also, you may consider timing a particular operation as a performance
>> metric, rather than counting the number of demodulated packets.
>>
> I was wondering if there are examples from which I can learn how to do
> this?

Sorry, I guess there isnt much in the way of examples.

You can time individual work functions by adding some code before an
after. We have some high resolution timers in
gruel/include/gruel/high_res_timers.h

I have also seen people time the block in a simple flow graph with a
null source, head, your_block, null_sink. You can time tb.run() and
compare run duration vs the non-vectorized code.

-Josh