JDK build questions

[John Rose]

On Apr 16, 2010, at 1:55 PM, Kelly O'Hair wrote:

> So often the raw performance comes down to the VM generated code

Yes, that's the main story.

Performance is strongly determined by code generated by the dynamic compiler (aka "JIT").

C++-generated instructions are rarely executed, apart from the GC.

If we find C++-generated code getting executed in a hot path, we take it over into either VM-compiled code or hand-written assembly.  (For an example of the latter, see the arraycopy stubs.)

The next most likely bottleneck, IMO, is memory system effects.

Occasionally there is a significant effect from the GC code written in C++, so the GC code gets a good share of tweaking.  (E.g., see oopDesc::size_given_klass and related functions.)

It's rare to find significant overheads in the other C++ code, except during startup.  (Therefore the classfile parsing code has received tuning.)

-- John