RFR(S) 8240205: Avoid PackageEntry lookup when loading shared classes

[Lois Foltan]

On 4/2/2020 8:58 PM, Calvin Cheung wrote:
> RFE: https://bugs.openjdk.java.net/browse/JDK-8240205
> webrev: http://cr.openjdk.java.net/~ccheung/jdk15/8240205/webrev.00/
>
> During loading of a shared class from a CDS archive, the PackageEntry 
> is being looked up in several places within the same call stack. This 
> RFE is to do the PackageEntry lookup at one place and then pass it 
> along to the subsequently called functions which need it.
>
> Perf improvement on loading approx. 2000 classes on linux:
>
> instr delta = -17930620 -0.6155%
> time delta = -6.311 ms -0.7516%
>
> Passed tiers1 - 4 testing.
>
> thanks,
>
> Calvin
>
>
Hi Calvin,

This looks good & promising on the numbers!  I have a slight concern 
that you've introduced yet another "get package entry from name" sort of 
function in SystemDictionaryShared. classfile/modules.cpp already 
contains a static method get_package_entry_by_name() but it operates on 
a package name not a class name.  Please consider moving 
SystemDictionaryShared::get_package_entry_from_class_name into 
ClassLoader near ClassLoader::get_package_from_class_name().  That seems 
like a more consistent place to add it that various areas of the JVM can 
take advantage of.

Thanks,
Lois