Added the following to the X10 Languages FAQ,
http://docs.codehaus.org/display/XTENLANG/X10+Language+Features+FAQ.
Why are all cores active when I run a sequential X10 program on
the Java backend?
X10 implements async using a user-space scheduler (a ForkJoin scheduler
in v2.0.4). This scheduler starts with a given set of workers (see How
do I control the size of the thread pool in a place?
<http://docs.codehaus.org/display/XTENLANG/X10+Language+Features+FAQ#X10LanguageFeaturesFAQ-THREADSPOOLSIZE>).
For the duration of the X10 program, "idle" workers are constantly
searching for work. In the Java backend, the number default to
availableProcessors(), hence all cores are busy.
How do I control the size of the thread pool in a place?
For the C++ backend, set the environment variable X10_NTHREADS to
control the number of initial workers in a place. For the Java backend,
provide the -INIT_THREADS command-line option. (This defaults to
availableProcessors().)
Note that the ForkJoin scheduler in X10 2.0.4 may create more workers if
the current worker suspends (e.g. to execute a when).
See X10 Runtime presentation at X10 Day
<http://docs.codehaus.org/download/attachments/140575067/X10_Runtime.pdf?version=2&modificationDate=1271426365763>
for more details.
Tetsu Soh wrote:
> Hello everyone,
>
> I run a serial Fibonacci program(without multi-activity programming) on
> a 24-core Linux box with Java back-end X10 2.0.4 and found that all
> cores were active. How it comes? Is it because the thread pool that
> employed in Java-back end is always working?
> And is there any way to control how many threads should be active in the
> thread pool in the case that I don't want all my cores are used to run
> the X10 program?
>
> Thank you in advance.
> -Tetsu
>
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