Forum: GNU Radio Scheduler Question

I've been reading through the code in gnuradio-core/runtime for a few 
days
to understand the internal workings of the gnuradio scheduler.  It seems 
to
me that gnuradio was originally based on a synchronous dataflow (sdf) 
model
of computation and the single thread schedule is an SDF sequential 
runtime
schedule, or a periodic admissible sequential schedule (PASS), and the
thread per block schedule is a parallel SDF scheduler, or a parallel
admissible parallel schedule (PAPS).

Does this sound like an accurate description of the schedulers and
underlying gnuradio model of computation or am I reading too much into 
it?
thanks

Hi Almohanad - From my (now old) memory of the GR runtime scheduler (STS 
and TBP), I believe you are roughly correct in the technical 
terminology, except that the schedules are not guaranteed to be 
periodic.  They are opportunistic / aperiodic: process as much data as 
"makes sense" given the blocks constraints and how much data is 
available and how much output space is available.  Tom (et.al.) have 
done some work on the TBP scheduler more recently than my memories, so 
maybe they have been tweaked to be truly periodic?

That said, I do not believe either scheduler was created specifically 
with those terms or concepts in mind; I believe the current scheduler(s) 
were programmed as they are because they work well and were original 
creations.  They might have been influenced by reading others works on 
SDF and the like, but I really doubt there was any true intent on 
recreating others works.

Again, these are memories that I believe are correct; but then who 
knows.  I believe Eric Blossom wrote both of the schedulers, and he's no 
longer around on this list to answer more officially (though I 
understand that folks do interact with him in person). - MLD

On Wed, Feb 27, 2013 at 9:06 AM, Michael Dickens <mlk@alum.mit.edu> 
wrote:
> Hi Almohanad - From my (now old) memory of the GR runtime scheduler (STS and 
TBP), I believe you are roughly correct in the technical terminology, except that 
the schedules are not guaranteed to be periodic.  They are opportunistic / 
aperiodic: process as much data as "makes sense" given the blocks constraints and 
how much data is available and how much output space is available.  Tom (et.al.) 
have done some work on the TBP scheduler more recently than my memories, so maybe 
they have been tweaked to be truly periodic?
>
> That said, I do not believe either scheduler was created specifically with those 
terms or concepts in mind; I believe the current scheduler(s) were programmed as 
they are because they work well and were original creations.  They might have been 
influenced by reading others works on SDF and the like, but I really doubt there 
was any true intent on recreating others works.
>
> Again, these are memories that I believe are correct; but then who knows.  I 
believe Eric Blossom wrote both of the schedulers, and he's no longer around on 
this list to answer more officially (though I understand that folks do interact 
with him in person). - MLD

Yeah, that about sums it up from my understanding of the history, too.
The single-threaded scheduler was basically a dataflow model and I'm
sure Eric used that concept to inform his design.

When it comes to the TPB scheduler, the task was to make GNU Radio
multi-threaded. So Eric adapted the STS one and rethought how it could
work in parallel with some push-pull concepts about how much data is
available on the input versus how much buffer space is available on
the output. At this point, I'm not sure any strict concepts of
scheduler theory were necessarily adhered to, though it wouldn't
surprise me to learn that it's similar to some standard model(s) of
computation (Eric has a long history in that area, so he would be well
aware of the various concepts, models, and ideas).

Tom