RFR: 8308118: Avoid multiarray allocations in AESCrypt.makeSessionKey

[David Schlosnagle]

On Mon, 15 May 2023 19:59:13 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> One of our services has a hot path with AES/GCM cipher reuse. The JDK code reinitializes the session key on that path, and [JDK-8308105](https://bugs.openjdk.org/browse/JDK-8308105) shows up prominently there. While [JDK-8308105](https://bugs.openjdk.org/browse/JDK-8308105) is being fixed, which would take a while, and would likely require multiple patches, we can work this issue around by avoiding the multiarray allocations in AESCrypt.makeSessionKey.
> 
> Example profile is in the bug.
> 
> On new benchmark and M1 Mac:
> 
> 
> Benchmark       Mode  Cnt    Score   Error  Units
> 
> # Before
> AESReinit.test  avgt   15  873,842 ± 6,911  ns/op
> 
> # After
> AESReinit.test  avgt   15  533,018 ± 4,048  ns/op
> 
> 
> Additional testing:
>  - [x] Benchmarks
>  - [x] macos-aarch64-server-release, `jdk_security`
>  - [ ] linux-x86_64-server-fastdebug, `tier1 tier2`
>  - [ ] linux-aarch64-server-fastdebug, `tier1 tier2`

src/java.base/share/classes/com/sun/crypto/provider/AESCrypt.java line 1369:

> 1367:         int BC = 4;
> 1368:         int[][] Ke = new int[ROUNDS + 1][]; // encryption round keys
> 1369:         int[][] Kd = new int[ROUNDS + 1][]; // decryption round keys

This is more a question of curiosity and likely beyond the scope of this PR/bug ID -- would it be beneficial to refactor this to allocate and operate over just two arrays, one for Ke and one for Kd, effectively removing the need for allocation in `expandToSubKey` as well?


int[] Ke = new int[4 * (ROUNDS + 1)];
int[] Kd = new int[4 * (ROUNDS + 1)];

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PR Review Comment: https://git.openjdk.org/jdk/pull/13996#discussion_r1194511682