RFR: 8349814: [leyden] Avoid uncommon traps in preload code

[Aleksey Shipilev]

On Tue, 11 Feb 2025 10:47:37 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Preload code is the C2 code we load very early, before it gets substituted by more advanced C2 code. We are seeing lots of uncommon traps from the preloaded code, though, which invalidates it too early. We can do precompile code without uncommon traps to alleviate this. 
> 
> Additional testing:
>  - [x] Ad-hoc perf tests (see comment below)
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`

Since this avoids excess C2 (re-)compilations, the major impact is on "user" time. This impact reflects to run-to-run times when we are short on available CPU cores:


Benchmark 1: build/linux-x86_64-server-release/images/jdk/bin/java -Xms64m -Xmx1g -XX:+UseParallelGC \
  -XX:CacheDataStore=JavacBenchApp.cds -cp JavacBenchApp.jar JavacBenchApp 50

# --- 32 cores

# Before: ~38 deopts from preload code
  Time (mean ± σ):     436.9 ms ±   9.0 ms    [User: 1162.8 ms, System: 148.6 ms]
  Range (min … max):   428.2 ms … 453.4 ms    10 runs

# After: ~0 deopts from preload code
  Time (mean ± σ):     438.2 ms ±   4.5 ms    [User: 828.9 ms, System: 131.0 ms]
  Range (min … max):   430.3 ms … 444.9 ms    10 runs

# --- 2 cores

# Before: ~30 deopts from preload code
  Time (mean ± σ):     531.0 ms ±  12.8 ms    [User: 846.1 ms, System: 117.8 ms]
  Range (min … max):   508.9 ms … 553.1 ms    10 runs

# After: ~0 deopts from preload code
  Time (mean ± σ):     510.4 ms ±  14.1 ms    [User: 803.7 ms, System: 115.0 ms]
  Range (min … max):   483.7 ms … 535.5 ms    10 runs

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PR Comment: https://git.openjdk.org/leyden/pull/38#issuecomment-2650438536