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Re: [Discuss-gnuradio] Flowgraph running in "fits and starts"

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Flowgraph running in "fits and starts"
Date: Sat, 04 Sep 2010 20:22:38 -0400
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On 09/04/2010 08:08 PM, Tom Rondeau wrote:
> On Sat, Sep 4, 2010 at 12:19 AM, Marcus D. Leech <address@hidden> wrote
> Like Eric said, remove the throttle or at least change the rate and
> that should clean things up.
> Tom
I also noted in the reply to Eric that I observe the same behaviour with
an external source that is producing 4800 symbols/second--so
  it's not the throttle *per se*, but rather the way that work "chunks"
get scheduled in Gnu Radio.  With a "fast" source, you dont find yourself
  in a situation where there aren't enough "chunks" to keep things busy.

But a very reasonable example would be something like a cross-band
digital repeater application, where bits/symbols would be arriving
  at the "channel rate", and need to leave the Tx in something at least
approaching real time--you certainly need to have a bit of
  elastic buffering to compensate for clock-skew between the two sides,
but several-tens-of-seconds of latency isn't likely to be very
  useful in the real world.

Note that I'm not criticizing anybody or anything.  I'm making
observations, and I *do* understand *why* it is the way it is.
  My little test flow-graph failed the "least astonishment test", which
is why I felt I needed to comment.

Would it be reasonable to open a discussion about this class of
flow-graph?  I think they can be characterized as flow-graphs with
  a low symbol rate, and high interpolation (which I think is where the
buffer-multiplier effect may be coming into play).  In such flow-graphs,
  would it be reasonable to be able to "tweak" the scheduler to deal
with this type of situation?  I have little insight into how the scheduler
  works in detail, but I think I understand the "fits and starts" that I
was observing.

So, is this a reasonable discussion topic?  Are other folks working on
"stuff" that will run into part of the performance diagram I ran
  into yesterday?  Or is everyone else working on high-event-rate type
signal chains?


Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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