Interface method calls are slow.

Tue Nov 16 20:05:00 GMT 1999

I wrote a small benchmark to time different types of method calls. The code is
available from http://waitaki.otago.ac.nz/~bryce/gcj/meth-inv-bench.tar.gz
The IBM JDK 1.1.8 gets:
no call: 181ms [18ns / call]
local: 287ms [28ns / call]
private: 163ms [16ns / call]
interface: 1506ms [150ns / call]
i/f after cast: 324ms [32ns / call]
abstract: 951ms [95ns / call]
abstract w/cast: 316ms [31ns / call]
native: 4645ms [464ns / call]
While gcj (compiled from source with -O3) gets:
no call: 97ms [9ns / call]
local: 734ms [73ns / call]
private: 606ms [60ns / call]
interface: 5890ms [589ns / call]
i/f after cast: 688ms [68ns / call]
abstract: 686ms [68ns / call]
abstract w/cast: 688ms [68ns / call]
native: 683ms [68ns / call]
I'm not too concerned about the differences between gcj and the VM here -
obviously IBM's JITC is doing a lot of clever optimization that doesn't
neccessarily apply to real-world situations, and maybe cannot even be done by an
ahead-of-time compiler.
BUT...
Why are interface calls so expensive compared to other calls in gcj? I remember
that there was talk a while back about changing the way interface calls are
compiled by gcj - were these change ever made? Slow interface calls will have a
significant impact on the performance of AWT, where every call to a component's
native peer is sent through the interfaces in java.awt.peer. Many other newwer
Java APIs are fairly interface-dependent as well. I am using a current libgcj.
It also appears that the private method call is not being inlined. I thought
that gcj was inlining private methods now?
regards
 [ bryce ]