RFR: 8224816: Provide os::processor_id() implementation for Mac OS

[Erik Österlund]

Hi Per,

Thanks for reviewing.

On 2019-05-28 09:46, Per Liden wrote:
> Hi Erik,
>
> On 5/27/19 12:05 PM, Erik Österlund wrote:
>> Hi,
>>
>> In order to port ZGC to Mac OS, we need to implement 
>> os::processor_id(), due to the use of CPU locals in ZGC.
>> I built an implementation that uses CPUID to get the APIC id, and 
>> from that determine a unique CPU id.
>> Note though that the APIC ids are split over a potentially larger 
>> number space than the number of processors.
>> In order to reliably translate APIC ids to CPU ids, I first use CPUID 
>> to query how many bits are being used
>> for APIC ids, and then create an array of integers covering that 
>> space. The array maps possible APIC id positions
>> to a unique processor id. The array is lazily populated with APIC id 
>> -> processor id mappings.
>> The specific CPUID leaf used to query this topology information is 
>> intel-specific, but that should be okay as all macs are Intel based.
>> I have tried this out on a number of macs with a mac port of ZGC (to 
>> be upstreamed soon), and it worked well.
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8224816
>>
>> Webrev:
>> http://cr.openjdk.java.net/~eosterlund/8224816/webrev.00/
>
> Just a few comments:
>
> * Maybe replace "cpu" with "processor" in variable names, since the 
> function is named processor_id().

Fixed.

> * Could we split out the setup of the array into a separate function 
> helper, like:
>
>   volatile int* mapping = get_apic_to_processor_mapping();

Fixed.

> * Move the declaration of "apic_to_cpu_mapping" and "next_cpu_id" out 
> of the function, to avoid the pthread_once initialization checks every 
> call?

Fixed.

New webrev:
http://cr.openjdk.java.net/~eosterlund/8224816/webrev.01/

Incremental:
http://cr.openjdk.java.net/~eosterlund/8224816/webrev.00_01/

Thanks,
/Erik

> cheers,
> /Per
>
>>
>> Thanks,
>> /Erik