Review Request: UseNUMAInterleaving

Igor Veresov igor.veresov at
Mon May 16 12:53:47 PDT 2011

On 5/16/11 11:21 AM, David Dabbs wrote:

The 2.6.19 requirement is there because we need the sched_getcpu() 
syscall to determine on which CPU we're running.

I guess it won't be hard to extend UseNUMAInterleaving to work on other 
OSes, including old Linuxes. You can, however, achieve the same effect 
by running the VM with "numactl -i all java <your-options>" or by 
turning interleaving on in BIOS in hardware.


> Could this flag help Linux systems with kernel<  2.6.19, or is that the
> minimum kernel needed for any JVM NUMA support?
> Unfortunately, we run CentOS 5.5 (2.6.18)
> Linux 2.6.18-194.17.4.el5 #1 SMP Mon Oct 25 15:50:53 EDT 2010
> x86_64 x86_64 x86_64 GNU/Linux
> and so -XX:+UseNUMA does not activate (at least not according to
> PrintFlagsFinal).
>> From
> In the Java HotSpot VM, the NUMA-aware allocator has been implemented to
> provide automatic memory placement optimisations for Java applications.
> Typically, every processor in the system has a local memory that provides
> low access latency and high bandwidth, and remote memory that is
> considerably slower to access. The NUMA-aware allocator is implemented for
> Solaris (>= 9u2) and Linux (kernel>= 2.6.19, glibc>= 2.6.1) operating
> systems, and can be turned on for the Parallel Scavenger garbage collector
> with the -XX:+UseNUMA flag. Parallel Scavenger remains the default for a
> server-class machine and can also be turned on explicitly by specifying the
> -XX:+UseParallelGC option. The impact of the change is significant: When
> evaluated against the SPEC JBB 2005 benchmark on an 8 chip Opteron machine,
> NUMA-aware systems gave about a 30% (for 32-bit) to 40% (for 64-bit)
> increase in performance.
> Thanks,
> David

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