RFR: JDK-8199406: Performance drop with Java JDK 1.8.0_162-b32

[Vladimir Kozlov]

Looks good. I have few comments.

You can remove old is_entry_point() which have the same code as new 
entry_point(). After changes it is used only in one place in 
CompiledIC::is_megamorphic(). It can be replace with NULL check of 
entry_point() result there. Add comment in vtableStubs.hpp for new method.

is_metadata_method field name should start with _ (this is Hotspot 
convention).

is_loader_alive() could be simplified since you have field now:

   inline bool is_loader_alive(BoolObjectClosure* is_alive) {
     Klass* k = is_metadata_method ? 
((Method*)_holder_metadata)->method_holder() : (Klass*)_holder_metadata;
     if (!k->is_loader_alive(is_alive)) {
       return false;
     }
     if (!_holder_klass->is_loader_alive(is_alive)) {
       return false;
     }
     return true;
   }

Thanks,
Vladimir

On 3/29/18 1:31 PM, Poonam Parhar wrote:
> Hello,
> 
> Please review the changes for the following bug that improve the nmethod 
> unloading times with a couple of optimizations.
> 
> JDK-8199406 <https://bugs.openjdk.java.net/browse/JDK-8199406>: 
> Performance drop with Java JDK 1.8.0_162-b32
> Webrev: http://cr.openjdk.java.net/~poonam/8199406/webrev.00/
> 
> This changeset includes two changes:
> 1. In /compiledIC.cpp, CompiledIC::is_icholder_entry()/ , we need to 
> determine if the code blob is an itable stub. With this change, before 
> linearly searching through all the VtableStub entries, we first check 
> whether the codeblob is a vtable or not. We now also parse through the 
> list entries only once rather than doing it twice in 
> /VtableStubs::is_entry_point()/ and /VtableStubs::stub_containing()/.
> 2. The second change helps avoid the virtual function calls in 
> CompiledICHolder::is_loader_alive(). CompiledICHolder now stores 
> information whether the metadata it holds is a method or a klass.
> 
> Testing:
> - Customer testing confirming that their class-unloading times drop from 
> 10s of seconds to an average of 0.75 secs.
> - mach5 jdk-tier1,jdk-tier2,jdk-tier3,hs-tier1,hs-tier2
> 
> Thanks,
> Poonam
>