http://stackoverflow.com/questions/7962155/how-can-you-detect-a-dual-core-cpu-on-an-andro
id-device-from-code says that availableProcessors() can under-report
the number of CPUs available on the device.
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Runtime.html#availableProcessors()
also says "This value may change during a particular invocation of the
virtual machine.".
>From the source, availableProcessors returns the available processors,
not necessarily all the physically present CPUs.
public int availableProcessors() {
// See http://austingroupbugs.net/view.php?id=339.
// _SC_NPROCESSORS_ONLN : The number of processors online
(capable of running processes).
// _SC_NPROCESSORS_CONF - The number of processors configured.
return (int) Libcore.os.sysconf(_SC_NPROCESSORS_ONLN);
}
On Android, when will _SC_NPROCESSORS_ONLN and _SC_NPROCESSORS_CONF
differ? Do any kernels restrict app code to a subset of the physically
available processors (using sched_setaffinity)?
What is the correct way to find the number of cpus on the device in
order to determine which optimizations to enable in my app? This needs
to include cpus that may currently be powered down if they will get
enabled once my optimization code starts executing.
Thanks,
Shri
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