[Pvfs2-developers] terminating state machines

[Phil Carns]

> 
> Thanks for the detailed explanation Phil.  I hadn't thought about the  
> context switches that might slow down flow.  I was primarily thinking  
> of something that would be cleaner, and easier to modify and test for  
> different scenarios.  If at some point I get around to playing with a  
> flow impl that uses the concurrent state machine framework, I'll open  
> up the discussion again to avoid any of the pitfalls you described.

Cleaner and easier to modify would be great!

I just remembered that there are a couple of test programs in the tree 
to look at the thread context switch overhead, in case they are helpful 
to figure out if it is still a concern:

pvfs2/test/io/job/thread-bench2.c
pvfs2/test/io/job/thread-bench3.c

One of those just goes through a bunch of iterations relaying a 
condition across threads to see how long it takes.  The second one does 
the same thing, except with 2 relays instead of one (to mimic the trove 
side of things).  I haven't run these on a decent machine in years.  I 
will also add a disclaimer that the test programs are old and quite 
possibly wrong :)

We also have the benefit of your small-io optimization now too, so it 
isn't quite as critical as it used to be for the flow to be able to keep 
the latency down on small transfers any more...

-Phil