Subj : Re: Lock Free -- where to start
To   : comp.programming.threads
From : chris noonan
Date : Fri Oct 14 2005 10:39 am

David Schwartz wrote:
>     The optimum number of concurrent threads is one per processor if the
> threads are CPU bound. I still don't understand what you think the
> connection between IOCP and lock efficiency is. Maybe it's obvious to you,
> but I don't see it. I'm genuinely curious.
I agree in principle about the optimum number of threads. However
when there is no synchronisation between the threads the
performance loss suffered by having a large number of threads
is so tiny as not to be measurable. My IOCP point was more
philosophical than technical: a "one thread good, many
threads bad" mantra has evolved through experience of
operating systems that take so many locks that multi-
threaded performance dives (that is my guess, I can't
be sure). IOCP is a means of reducing the number of
threads running, at the cost of software complexity.

> In any event, if you don't have 1000 CPUs, it's pretty dumb for you to
> have 1000 ready-to-run threads. If you do have 1000 CPUs, it's really just
> the time it takes to do *one* context switch.
It's dumb to run 1000 threads if you expect performance
deterioration. If I were programming a thousand-client-server
under Microsoft Windows, I'd use IOCP. What I am interested
in is the reason for the performance deterioration.

Chris

.