Re: [Discuss-gnuradio] sustainable gnuradio MFLOPS for streaming processing

[Nathan West]

On Thu, Jul 11, 2013 at 6:13 PM, LD Zhang <address@hidden> wrote:
> Hi, Please my comment below:
>
> You can probably get a rough estimate of the lower limit of your processors
> ability to do something like an FIR filter with some simple
> calculations:
> A 10-point FIR filter needs to do 10 multiplies and 9 additions.
> Blissfully ignoring branching that's 19 instructions for each output.
> So let's say we've got a simple FIR filter that outputs the same sample rate
> as it inputs.
>
> Using the table in here:
> http://en.wikipedia.org/wiki/Instructions_per_second it looks like modern
> CPUs clocked around 1GHz should expect between 2-5 IPS / (1/clock speed).
> Pick your favorite (I'm guessing you're on older hardware so let's go with
> 2). 2 * 1GHz = 2000 MIPs. So you can process 1M samples through a very
> poorly implemented 10-tap FIR filter. That in itself is also a pretty poor
> estimate. I see Marcus just replied as well and as he said, the best way to
> *know* is just to try it out on your hardware; there's no substitute for
> that.
>
>
>>>> I am confused: 10-tap FIR according to the above is 19 IPs, so 1M
> samples correspond to 19 MIPS, much below the 2000 MIPS limit?
> Am I missing something?
>
> LD
>

Hmm, I guess you're right. It's not too important because the actual
estimate wouldn't be close to anything close to what you would see.
The point is there is no easy answer (other than just running
something to see if it works), but you might be able to come up with a
rough estimate if you really need to and your application is really
simple. You should probably ignore my lousy attempt :-P. I came up
with it on the fly... There's also the issue of how long it takes
those instructions to execute.

-Nathan