Wenlong Li wrote:
Hey, all,
I instrumented the Harmony startup module: Harmony VM creation in
JNI_GetCreatedJavaVMs of jni.cpp. This module is responsible for
creating VM, which includes classpath setting (jar file parsing and
handling), class loading & prepariing & initializing, compilation,
etc. In my test bed (2.8GHz Core 2 Quad-core, WinXP OS), Harmony will
take 170ms to creating VM in client mode (RI is much faster than
Harmony, but I don't have the exact number for its VM creation part).
For VM creation module, most time is spent in dll loading (in
vm_init1), classpath parsing and jar file processing (in
bootstrap_initial_java_classes), class file loading (basic and system
classes in preload_classes and initialize_system_class_loader], and
compilation (jet part).
To reduce the compilation time, I was wondering to postpone the
compilation phase, that means, can interpreter be used in startup
phase? I just compared the VM creation performance between client and
interpreter modes, and found interpreter is 20% faster than client
mode.
Another optimization in my mind is to reduce the disk I/O time, where
I could merge all jars into one big jar to provide .class file.
all-in-one jar may break the whole modular architecture. It's the one of
the most important features of Harmony that anyone can easily customize
the runtime, one big jar is hard to do it.
I didn't see the process of preload and initialize classes, and which
classes are required by vm startup, maybe we could pack these necessary
classes to a bootstrasp.jar, only load this jar when vm startup, other
jars could loaded on demand?
Another possible approach is to pre-load these jar files into disk
cache or memory (put all jars into /dev/shm directory under Linux OS).
What do you think? Any comments or suggestion are welcome and appreciated.
Thx, Wenlong
