[PATCH] Implement -XX:+BindGCTaskThreadsToCPUs for Linux

[Roman Kennke]

I implemented the other two missing functions in os_linux.cpp
(distribute_processes() and bind_to_processor() ) which implement
support for the -XX:+BindGCTaskThreadsToCPUs option (together with -XX:
+UseParallelGC), which distributes & binds GC worker threads to
different processors.

The implementation is adopted from os_solaris.cpp. In particular
assign_distribution() is almost 1:1 copy (except for the type diff
processor_t vs. uint). It could be worth extracting this into a shared
method, but on the other hand, there is potential for divergence (for
example, for NUMA support. See my related question here:
http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2012-July/004751.html ).

Just like the implementation for Solaris, we first check if we are
running in a CPU set, and take this as a basis. I did not implement the
other case though, it seems like a really rare fallback (processes that
do not have any particular processor affinity return affinity with all
processors set). Plus, if that call to pthread_getaffinity_np() does not
work, it seems likely that the following call to
pthread_setaffinity_np() doesn't work either (because lack of
permissions or lack of support in the kernel or such). Please let me
know if you think it's worth to implement this case anyway and use the
set of all online processors then.

Opinions about that patch?

http://cr.openjdk.java.net/~rkennke/linux_gc_workers/webrev.00/

Kind regards,
Roman