Re: CPUs, thread pools, and wasted time.
Zig wrote:
If that theory doesn't pan out, on Windows: Task Manager / Process
Explorer can be used to set the processor affinity for your java.exe
process. I'm sure google will turn up the command to do the same on Linux.
I find this question (determining processor affinity for JVM threads) very
interesting and relevant, as just about every general-purpose computer being
made any more is multi-processor. I spent a good bit of time googling around,
and even the most Java-esque writers spoke only of OS utilities for setting
processor affinity. I found nothing yet on doing it via the JVM. Well, not
quite nothing - there's a few places that hint that ThreadLocal variables will
improve processor locality of references.
Setting affinity for the EXE probably won't help distribute different threads
among different processors.
At Ye Big Organization where I work and there's a whole lot of IBM WebSphere
they coerce JVMs to a particular processor and load balance among the JVMs. I
don't think they divide threads, though.
Even if you could split threads, every time those threads share data or
synchronize or whatever they need to do in coordination you'd have a non-local
memory reference somewhere. Putting a whole JVM on a core would obviate that,
at least somewhat. You'd have to balance that against the ability to
parallelize your algorithm, hoping that the parallelization ("p13n"?) will
improve things more than inter-processor memory access will hurt them.
Much of the wisdom I encountered about multi-processor Java involved using
parallel garbage collection (GC). Since GC can impose a major drain on
performance, this may be a very useful tip.
Daniel Dyer wrote:
Apple 1.5.0_07 on OS X.
Perhaps either OS X or that particular JVM has its own set of rules about
processor affinity.
--
Lew