RFR(s): 8235410: Enable handshakes on Linux x86 (32-bit)

[Robbin Ehn]

Thanks David!

On 2019-12-05 22:36, David Holmes wrote:
>> diff -r 636d71e53732 src/hotspot/cpu/x86/globals_x86.hpp
>> --- a/src/hotspot/cpu/x86/globals_x86.hpp    Wed Dec 04 10:26:32 2019 
>> +0100
>> +++ b/src/hotspot/cpu/x86/globals_x86.hpp    Thu Dec 05 14:13:57 2019 
>> +0100
>> @@ -89,12 +89,7 @@
>>
>>   define_pd_global(intx, InitArrayShortSize, 8*BytesPerLong);
>>
>> -#if defined(_LP64) || defined(_WINDOWS)
>>   define_pd_global(bool, ThreadLocalHandshakes, true);
>> -#else
>> -// get_thread() is slow on linux 32 bit, therefore off by default
>
> Why would get_thread be slow on linux 32-bit? Have we discussed this 
> when handshakes went in? I'm feeling surprised now to see only 32-bit 
> Linux was disabled.

You actually explained it RFR for 32-bit TLH:

"Thread::current() already uses compiler-based TLS. get_thread (on 
non-Windows x86) make a VM call to Thread::current(). If we want to get 
faster here we have to introduce compiler specific hooks directly into 
the TLS implementation (not nice to do initially or maintain). "

:)

/Robbin


>
> Thanks,
> David
>
>> -define_pd_global(bool, ThreadLocalHandshakes, false);
>> -#endif
>>
>>   #define ARCH_FLAGS(develop, \
>>                      product, \