RFR: 8232651: Add implementation of os::processor_id() for Windows

[Bob Vandette]

> On Oct 21, 2019, at 4:14 PM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
> 
> Hi Bob,
> 
> On 2019-10-21 16:41, Bob Vandette wrote:
>> Have you considered using GetCurrentProcessorNumberEx so you can handle a system with more than 64 CPUs?
> 
> If I understand the Windows documentation I linked to below, you need to opt-in to multi-groups to be able to take advantage of more than 64 logical processors. I couldn't find any code that explicitly scheduled threads to other groups than the one the JVM starts in. Neither os::processor_count() nor os::active_processor_count() includes the number of CPUs outside of the current group. If those observations are correct, I don't think it would be appropriate to use GetCurrentProcessorNumberEx without also updating the other Windows code.
> 
> Do you agree with this assessment?

I though it might be better to just call the extended API in order to at least prepare any new OS:: interfaces for the
future but it does appear that such support is more involved so I’m good with your assessment.

Bob.


> 
> Thanks,
> StefanK
> 
>> 
>> Bob.
>> 
>> 
>>> On Oct 21, 2019, at 10:23 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
>>> 
>>> Hi all,
>>> 
>>> Please review this patch to add an implementation of os::processor_id() for Windows.
>>> 
>>> https://cr.openjdk.java.net/~stefank/8232651/webrev.01/
>>> https://bugs.openjdk.java.net/browse/JDK-8232651
>>> 
>>> We need an implementation of this function on Windows, to be able to run ZGC there.
>>> 
>>> Note that GetCurrentProcessorNumber only "returns the processor number within the processor group to which the logical processor is assigned". AFAICT, there's no support for multi-groups in HotSpot, and therefore this seems like an adequate function to use.
>>> 
>>> See this page for more information about processor groups:
>>> https://docs.microsoft.com/en-us/windows/win32/procthread/processor-groups
>>> 
>>> Thanks,
>>> StefanK
>