[12] RFR(XXS): JDK-8196950: AARCH64 - Add VM flags presets for Cavium Thunder X2 CPU

[Dmitry Chuyko]

Hi Andrew,

On 11/1/18 12:47 PM, Andrew Dinn wrote:
> On 31/10/18 17:40, Dmitry Chuyko wrote:
>> Please review small defaults correction.
>>
>> rfe: https://bugs.openjdk.java.net/browse/JDK-8196950
>> code:
>>
>> diff -r 16950b2eaebf src/hotspot/cpu/aarch64/vm_version_aarch64.cpp
>> --- a/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp    Tue Oct 30
>> 09:13:00 2018 -0400
>> +++ b/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp    Wed Oct 31
>> 20:33:41 2018 +0300
>> @@ -219,7 +219,7 @@
>>       }
>>   #ifdef COMPILER2
>>       if (FLAG_IS_DEFAULT(UseFPUForSpilling)) {
>> -      FLAG_SET_DEFAULT(UseFPUForSpilling, true);
>> +      FLAG_SET_DEFAULT(UseFPUForSpilling, false);
>>       }
>>   #endif
>>     }
>>
>> Having "-XX:+AvoidUnalignedAccesses -XX:+UseSIMDForMemoryOps
>> -XX:-UseFPUForSpilling" as a default works (in general) better for
>> SPECjvm and SPECjbb.
> That's fine as a goal. However, I don't think this is the right patch.
>
> Flag UseFPUForSpilling is defined in
> src/hotspot/share/opto/c2_globals.hpp as follows:
>
>    product(bool, UseFPUForSpilling, false,
>     \
>            "Spill integer registers to FPU instead of stack when
> possible")  \
>
> In other words the global default is already false. Indeed, that is the
> the default used for the other AArch64 variants.
>
> So, the correct patch is to remove the whole if clause. Of course, you
> should also remove the surrounding ifdef COMPILER2 endif that brackets it.

That's an option. Though "default" (false) and "false" are not exactly 
the same, in the sense of explicitly expressing the difference in 
benchmarks score, we'll have history for that.

Webrev with updated patch: 
http://cr.openjdk.java.net/~dchuyko/8198294/webrev.00/

>
> regards,
>
>
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
> Red Hat UK Ltd
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