[viff-devel] Mystery of the quadratic running time solved?

[Martin Geisler]

Marcel Keller <mkeller at cs.au.dk> writes:

>> You're talking about this two-threaded solution as if it is something
>> that exists and will solve all our problems...
>
> No, for now, it's just an imagination in my mind, a proposal for the
> next meeting, and a strong feeling that it's the right way to do it.

Yeah, I think it would help too.

>> But I still haven't seen it, and I would like to see how you can
>> cleanly seperate the work of the two threads. I'm afraid that the
>> threads will be alternating between working and waiting on the other
>> thread in such a way that we could just as well use one thread.
>
> My idea is that the Twisted main loop runs in one thread and most of
> the VIFF code in the other. The Twisted thread only waits for I/O and
> the VIFF thread only waits if there is no work to be done.

It's funny -- then we'll have sort of two event loops.

> If the group decides to give this idea a try, I would be happy to
> implement it. I would claim that it can be done in one or two weeks.

So you'll have something when I get back from PKC? :) Seriously, I think
you're right, the code is fairly well partitioned already, so we should
be able to make this change without too much trouble.

>> Also, threading in Python is unfortunately not optimal :-( The Python
>> VM will use a single thread to execute the bytecode, even when using
>> multiple thread in Python. It is only if the threads do things
>> blocking for I/O that you will see a performance increase by using
>> multiple threads.
>
> I'm aware that Python only runs on one CPU, a friend pointed that out
> to me today. However, the Twisted thread mentioned above would block
> on I/O.

Right, that should help us! Janus has been looking more into Python
threads, so be sure to discuss it with him too.

-- 
Martin Geisler

VIFF (Virtual Ideal Functionality Framework) brings easy and efficient
SMPC (Secure Multiparty Computation) to Python. See: http://viff.dk/.
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