Re: multi-core CPU and multithreading
roger.jakobsen@gmail.com wrote:
I don't think the old JVM will fully utilize all cores. When my
Eclipse hangs, or "works", it will never chew more than 25 % of my
processor power ;) As you can probably guess I'm working on a 4 core
platform.
Eclipse? It's hard to draw conclusions when you're working within the nest of
the IDE. You've got debug compiles, non-optimized JVM settings, low-level IDE
hooks and the like going on.
A few simple tips:
-The number of simultaneously active threads should be less than the
number of hardware threads.
This directly contradicts the advice given in the link you provided, which says,
Number of simultaneously active software threads should be >= number of hardware threads.
Bear in mind that you can more threads *open* than you have processors for
some applications, e.g., I/O-bound processes.
-You should minimize writes to shared data since the processor must
acquire data ownership. This usually
means a write to plus a read from long-latency memory.
That depends - many writes are uncontended and the JVM will optimize the locks
(on recent Java platforms).
-Shared data reads are not expensive
Unless there's a cache miss or the read has to access local memory from a
different CPU's local RAM region.
Read more at:
http://it.sun.com/sunnews/events/2007/sept/jc07/pdf/Milano_JavaTrack1/TD_MILAN_Intel_Guermonprez.pdf
Read more at IBM DeveloperWorks and all over Sun, too.
--
Lew