Performance regression in BuiltinClassLoader?

[Eirik Bjørsnøs]

I also measured the actual startup time of Spring Petclinic to assess
real-life impact. Although there is some variance from run to run, it does
seem to regress:

15: Typical startup time 7500 - 7800 ms
17: Typical startup time: 8100 - 8700 ms

Eirik.

On Mon, Jan 18, 2021 at 7:34 PM Eirik Bjørsnøs <eirbjo at gmail.com> wrote:

>
> Hello,
>
> I've been looking into ZipFile again with the aim to speed up typical
> enterprise classloading / resource lookups.
>
> To test the performance impact of my changes, I made a benchmark which
> creates an EnterpriseClassLoader (subclass of URLClassLoader) with the jar
> files in Spring Petclinic (89 jars with ~30k entries total).
>
> (This is intentionally implemented using a plain main method with no JMH
> or warmup since I want to measure a representative cold application startup)
>
> The benchmark measures the time needed to call getResource 30K times, once
> for each entry name.
>
> Using 15.0.1, this completes in ~1700 ms
> Using 17 master, it completes in 12851 ms
>
> If I run the benchmark from the classpath instead of as a module, the
> result is even worse:
>
> 15: 1724 ms
> 17: 21885 ms
>
> If also measure GC collections and times, and get the following:
>
> 15:
> Collections: 4
> Collection time: 12 ms
>
> 17:
> Collections: 24
> Collection time: 44 ms
>
> (However, a JHM with -prof gc indicates that both 17 and 15 allocate
> ~5.6Kb/getResource after warmup, so not convinced this needs to be
> allocation related)
>
> The EnterpriseClassLoader is a bit clever in that it can perform lookups
> using different strategies: Regular parent-first, self-only, or use the
> bootstrap / platform system classloaders directly.
>
> Here are the results on 17 using each strategy (benchmark on class path):
>
> PARENT_DELEGATION: 23111 ms
> SELF_ONLY: 428 ms
> BOOTSTRAP: 8131 ms
> PLATFORM: 15149 ms
> SYSTEM: 20628 ms
>
> Here are the same results on 15:
>
> PARENT_DELEGATION: 1691 ms
> SELF_ONLY: 393 ms
> BOOTSTRAP: 579 ms
> PLATFORM: 908 ms
> SYSTEM: 1368 ms
>
> Note that the delegation chain is Enterprise -> System -> Platform ->
> Bootstrap.
>
> Interesting to note that URLClassLoader itself does not seem to regress
> much when only looking up its own resources, while delegating up the chain
> does.
>
> Has there been any significant work in class loading / resource lookup
> since 15.0.1 that could help explain this regression?
>
> Eirik.
>
>
>