[Discuss-gnuradio] different CPU loads with 2 similar GRC graphs

[Achilleas Anastasopoulos]

I am comparing the following 2 systems on GRC:

[source] --> [block A] --> [sink]

and

[source] --> [block A] -->[sink]
     |___________________^

where [block A] is a very CPU-intensive SP block, source and sink are
very simple SP blocks,
and neither source nor sink set the sample rate, neither do i have any
throttle in the graph (intentionally).

When I run the first configuration on a 2-core machine
I get  2 CPU traces that alternate between 100% and 20%
for large chunks of time which means that the thread that is running
A overwhelms the system.

So far so good.

When I run the second configuraiton i get 2 CPU traces that alternate
around a load of
65% without any of them touching 100% (except occasionally) which seems like a
more "normal" situation.

So I have 2 questions:

1) why is it that the system does not "crash" even in the absense of a throttle?
2) why is it that the 2nd configuration results in a lower overall load?

thanks
Achilleas