RFR: 8317538: Potential bottleneck in Provider::getService: specjvm2008::crypto.rsa have scalability issue for high vCPU numbers

[Vladimir Ivanov]

On Fri, 25 Oct 2024 18:18:16 GMT, Vladimir Ivanov <vaivanov at openjdk.org> wrote:

> This patch remove access to the shared variable to fix scalability issue in the multithread environment. According to testing by the specjvm2008::crypto.rsa the one thread performance reduced for less than 1% while the score for the multithread run increased in ~2x. For the 2 socket system with Xeon 8480+ numbers looks as:
> •	1 thread: 643.15 for original version vs 642.54 for patched one;
> •	224 threads: 22446.19 for original vs 46147.41 for patched.
> The RSABench microbenchmark reports no score changes for the 1 thread (average for all testcases) and 2.4% improvement for the 224 threads.

With the non-static field the reported score similar to the score with removed variable. I.e. the minimal changes 
-     private static volatile ServiceKey previousKey =
+    private transient ServiceKey previousKey =
gives a little bit smaller score for the 224 threads runs vs variable remove but scores close to run-to-run variation.
For the first glance, this update should have no negative impact for performance for other apps/ benchmarks.
Reported scores for current/removed var/instance var for 1 thread runs are 641.98/639.4/644.47 and for 224 threads are 21271.09/47841.5/42045.25.

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PR Comment: https://git.openjdk.org/jdk/pull/21719#issuecomment-2445369468