RFR: 8296507: GCM using more memory than necessary with in-place operations
James Baker
duke at openjdk.org
Wed Nov 16 16:21:55 UTC 2022
On Sun, 13 Nov 2022 02:54:10 GMT, Anthony Scarpino <ascarpino at openjdk.org> wrote:
> I would like a review of an update to the GCM code. A recent report showed that GCM memory usage for TLS was very large. This was a result of in-place buffers, which TLS uses, and how the code handled the combined intrinsic method during decryption. A temporary buffer was used because the combined intrinsic does gctr before ghash which results in a bad tag. The fix is to not use the combined intrinsic during in-place decryption and depend on the individual GHASH and CounterMode intrinsics. Direct ByteBuffers are not affected as they are not used by the intrinsics directly.
>
> The reduction in the memory usage boosted performance back to where it was before despite using slower intrinsics (gctr & ghash individually). The extra memory allocation for the temporary buffer out-weighted the faster intrinsic.
>
>
> JDK 17: 122913.554 ops/sec
> JDK 19: 94885.008 ops/sec
> Post fix: 122735.804 ops/sec
>
> There is no regression test because this is a memory change and test coverage already existing.
It's possibly worth noting that while this is merely fixing a regression for x86, it's very likely a decent sized performance improvement on arm64, where intrinsics for AES-GCM (depending on JVM vendor) aren't added until after Java 17.
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PR: https://git.openjdk.org/jdk/pull/11121
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