RFR: 8309390: [JVMCI] improve copying system properties into libgraal

[Doug Simon]

On Fri, 2 Jun 2023 20:32:14 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> This PR improves the startup time for libgraal by speeding up how `VM.savedProps` is copied into libgraal. This data structure is now serialized to a native buffer directly from C++ and the native buffer is then directly decoded by libgraal.
> 
> ## Times
> 
> The basic benchmarking below shows that this change brings the time for a nop Java app with eager libgraal initialization (2) down to almost the same time as lazy libgraal initialization (1). The latter typically means no libgraal initialization happens as a top tier JIT compilation is never scheduled in such a short running app.
> 
> 
> public class Nop {
>     public static void main(String[] args) {}
> }
> 
> 
> (1) Baseline (no options):
> 
>> for i in (seq 10); java Nop; end
>         0.05 real         0.04 user         0.01 sys
>         0.04 real         0.03 user         0.01 sys
>         0.04 real         0.03 user         0.01 sys
>         0.04 real         0.03 user         0.01 sys
>         0.03 real         0.03 user         0.00 sys
>         0.04 real         0.03 user         0.01 sys
>         0.04 real         0.03 user         0.00 sys
>         0.03 real         0.03 user         0.00 sys
>         0.04 real         0.03 user         0.01 sys
>         0.03 real         0.03 user         0.00 sys
> 
> 
> (2) Eagerly initialize libgraal (with PR):
> 
>> for i in (seq 10); /usr/bin/time java -XX:+EagerJVMCI Nop; end
>         0.06 real         0.04 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
>         0.05 real         0.03 user         0.01 sys
> 
> 
> (3) Eagerly initialize libgraal (without PR):
> 
>> for i in (seq 10); /usr/bin/time java -XX:+EagerJVMCI Nop; end
>         0.11 real         0.08 user         0.02 sys
>         0.08 real         0.06 user         0.01 sys
>         0.08 real         0.07 user         0.01 sys
>         0.10 real         0.07 user         0.01 sys
>         0.08 real         0.06 user         0.01 sys
>         0.10 real         0.07 user         0.01 sys
>         0.08 real         0.07 user         0.01 sys
>         0.08 real         0.07 user         0.01 sys
>         0.08 real  ...

src/java.base/share/classes/jdk/internal/util/SystemProps.java line 62:

> 60:      * are initialized by VersionProps.java-template.
> 61:      *
> 62:      * @return a Properties instance initialized with all of the properties

I took the liberty of correcting this javadoc to reflect the code.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/14291#discussion_r1215453699