RFR: 8273297: AES/GCM non-AVX512+VAES CPUs suffer after 8267125

[Smita Kamath]

On Tue, 14 Sep 2021 13:31:19 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Performance dropped up to 10% for 1k data after 8267125 for CPUs that do not support the new intrinsic. Tests run were crypto.full.AESGCMBench and crypto.full.AESGCMByteBuffer from the jmh micro benchmarks.
>> 
>> The problem is each instance of GHASH allocates 96 extra longs for the AVX512+VAES intrinsic regardless if the intrinsic is used. This extra table space should be allocated differently so that non-supporting CPUs do not suffer this penalty. This issue also affects non-Intel CPUs too.
>
> It seems to me there's a serious problem here. When you execute the galoisCounterMode_AESCrypt() intrinsic, I don't think there's a limit on the number of blocks to be encrypted. With the older intrinsic things are not so very bad because the incoming data is split into 6 segments. But if we use this intrinsic, there is no safepoint check in the inner loop, which can lead to a long time to safepoint, and this causes stalls on the other threads.
> If you split the incoming data into blocks of about a megabyte you'd lose no measurable performance but you'd dramatically improve the performance of everything else, especially with a concurrent GC.

@theRealAph Thank you for the comment above. I will look into this issue.

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PR: https://git.openjdk.java.net/jdk/pull/5402