RFR: 8308804: Improve UUID.randomUUID performance with bulk/scalable PRNG access

[Brett Okken]

On Wed, 24 May 2023 19:36:44 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> UUID is the very important class that is used to track identities of objects in large scale systems. On some of our systems, `UUID.randomUUID` takes >1% of total CPU time, and is frequently a scalability bottleneck due to `SecureRandom` synchronization.
> 
> The major issue with UUID code itself is that it reads from the single `SecureRandom` instance by 16 bytes. So the heavily contended `SecureRandom` is bashed with very small requests. This also has a chilling effect on other users of `SecureRandom`, when there is a heavy UUID generation traffic.
> 
> We can improve this by doing the bulk reads from the backing SecureRandom and possibly striping the reads across many instances of it. 
> 
> 
> Benchmark               Mode  Cnt  Score   Error   Units
> 
> ### AArch64 (m6g.4xlarge, Graviton, 16 cores)
> 
> # Before
> UUIDRandomBench.single  thrpt   15  3.545 ± 0.058  ops/us
> UUIDRandomBench.max     thrpt   15  1.832 ± 0.059  ops/us ; negative scaling
> 
> # After
> UUIDRandomBench.single  thrpt   15  4.421 ± 0.047  ops/us 
> UUIDRandomBench.max     thrpt   15  6.658 ± 0.092  ops/us ; positive scaling, ~1.5x
> 
> ### x86_64 (c6.8xlarge, Xeon, 18 cores)
> 
> # Before
> UUIDRandomBench.single  thrpt   15  2.710 ± 0.038  ops/us
> UUIDRandomBench.max     thrpt   15  1.880 ± 0.029  ops/us  ; negative scaling 
> 
> # After
> Benchmark                Mode  Cnt  Score   Error   Units
> UUIDRandomBench.single  thrpt   15  3.099 ± 0.022  ops/us
> UUIDRandomBench.max     thrpt   15  3.555 ± 0.062  ops/us  ; positive scaling, ~1.2x
> 
> 
> Note that there is still a scalability bottleneck in current default random (`NativePRNG`), because it synchronizes over a singleton instance for SHA1 mixer, then the engine itself, etc. -- it is quite a whack-a-mole to figure out the synchronization story there. The scalability fix in current default `SecureRandom` would be much more intrusive and risky, since it would change a core crypto class with unknown bug fanout.
> 
> Using the bulk reads even when the underlying PRNG is heavily synchronized is still a win. A more scalable PRNG would benefit from this as well. This PR adds a system property to select the PRNG implementation, and there we can clearly see the benefit with more scalable PRNG sources:
> 
> 
> Benchmark               Mode  Cnt   Score   Error   Units
> 
> ### x86_64 (c6.8xlarge, Xeon, 18 cores)
> 
> # Before, hacked `new SecureRandom()` to `SecureRandom.getInstance("SHA1PRNG")`
> UUIDRandomBench.single  thrpt   15  3.661 ± 0.008  ops/us
> UUIDRandomBench...

src/java.base/share/classes/java/util/UUID.java line 255:

> 253:                     // initializations, and thus false sharing between reader threads.
> 254:                     random.nextBytes(buf);
> 255:                     for (int c = 0; c < BUF_SIZE; c += UUID_CHUNK) {

I think this could be faster by using a ByteBuffer (or VarHandle) to process as longs.

https://mail.openjdk.org/pipermail/core-libs-dev/2023-March/101249.html

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PR Review Comment: https://git.openjdk.org/jdk/pull/14135#discussion_r1206118465