[Discuss-gnuradio] Memory oinking

[Marcus D. Leech]

I have a simple flow-graph,

A USRP, single channel, and a large FFT block, followed by a "vector to
stream", and a file-output block.

The FFT is 8M points, which for complex float samples, give something
like a 64M memory footprint.

But I'm finding that the virtual size of the resulting process is
4.5GB!, with an RSS of about 2.3G.

This seems larger than you'd expect, by a fairly large factor!

For comparison, I have a C program that processes the samples created by
the Gnu Radio "front end",
  which has:

      120 8M buffers (unsigned char)
      2 x 8M buffers (float)

The virtual size of this process is only about 1G, with a similar RSS
(it touches those buffers very
  regularly!).

It seems to me that there only needs to be perhaps a couple of buffers
per block inside Gnu Radio,
  which at worst gives you something like 8 complex buffers (about 64M
per buffer for complex float)
  in my flow-graph. Why the massive hugeness in memory footprint?

Now, I'll agree that memory is *cheap* these days, but scaling my
application is going to be limited
  by what Gnu Radio is capable of, rather than my back-end C program.

-- 
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org