[15] RFR (S): 8238696: x86: Enumerate all detected CPU features in VM_Version feature string

[David Holmes]

On 11/02/2020 9:47 pm, Vladimir Ivanov wrote:
> Updated webrev:
>    http://cr.openjdk.java.net/~vlivanov/8238696/webrev.02/
> 
> CPU feature string verification in vm_version_x86.cpp requires some 
> additional handling in CPUInfo [3] to ignore trailing dot.

Now I'm wondering about using the dot as a terminator. Doesn't the 
return value from jio_snprintf tell you whether you exceeded the buffer?

David
-----

> Best regards,
> Vladimir Ivanov
> 
> On 10.02.2020 17:12, Vladimir Ivanov wrote:
>> Thanks for taking a look, David.
>>
>> Updated webrev:
>>    http://cr.openjdk.java.net/~vlivanov/8238696/webrev.01/
>>
>>>> http://cr.openjdk.java.net/~vlivanov/8238696/webrev.00/
>>>> https://bugs.openjdk.java.net/browse/JDK-8238696
>>>>
>>>> Abstract_VM_Version::features_string() doesn't contain all the CPU 
>>>> features detected by the JVM on x86 (for example, for AVX-512 only 
>>>> AVX-512F is included as "evex").
>>>>
>>>> The fix adds missing features to the list [1].
>>>
>>> The function naming that you have changed for 
>>> supports_avx512_vpclmulqdq was explicitly requested by Vladimir K.:
>>>
>>> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2019-December/036326.html 
>>>
>>>
>>> If anything I would suggest supports_vpopcntdq() should have the 
>>> avx512 part added.
>>
>> Makes sense. Also, decided to rename VNNI, VAES, and VBMI2. They are 
>> listed in the manual as part of AVX512.
>>
>>> The actual expansion of the feature string seems okay. It does make 
>>> me wonder why these items have been left out previously.
>>
>> I believe it was just overlooked. Added a comment near cpu feature 
>> constant declarations.
>>
>> Also, introduced a check to ensure the temporary on-stack buffer is 
>> large enough.
>>
>> Best regards,
>> Vladimir Ivanov
>>>
>>> Thanks,
>>> David
>>>
>>>> Testing: manual (-Xlog:os+cpu=trace output on different hardware),
>>>>           hs-precheckin-comp, hs-tier1, hs-tier2
>>>>
>>>> Best regards,
>>>> Vladimir Ivanov
>>>>
>>>> [1] $ java -Xlog:os+cpu=trace -XX:UseAVX=3 -version
>>>>
>>>> ...
>>>> [0.010s][info][os,cpu] UseSSE=4  UseAVX=3  UseAES=1  MaxVectorSize=64
>>>> ...
>>>> [0.011s][info][os,cpu] CPU:total 8 (initial active 8) (4 cores per 
>>>> cpu, 2 threads per core) family 6 model 85 stepping 4, cmov, cx8, 
>>>> fxsr, mmx, sse, sse2, sse3, ssse3, sse4.1, sse4.2, popcnt, 
>>>> vzeroupper, avx, avx2, aes, clmul, erms, rtm, 3dnowpref, lzcnt, ht, 
>>>> tsc, bmi1, bmi2, adx, avx512f, avx512dq, avx512cd, avx512bw, 
>>>> avx512vl, fma, clflush, clflushopt, clwb
>>>> ...
>>>> [0.011s][info][os,cpu] flags        : fpu vme de pse tsc msr pae mce 
>>>> cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 
>>>> ss ht syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon 
>>>> rep_good nopl xtopology cpuid tsc_known_freq pni pclmulqdq vmx ssse3 
>>>> fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer 
>>>> aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch 
>>>> cpuid_fault invpcid_single pti ssbd ibrs ibpb stibp tpr_shadow vnmi 
>>>> flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 
>>>> erms invpcid rtm mpx avx512f avx512dq rdseed adx smap clflushopt 
>>>> clwb avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves arat 
>>>> umip pku ospke md_clear
>>>> ...