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From "Wenlong Li" <wenl...@gmail.com>
Subject [performance] Startup cost is high for Harmony (HARMONY-6002)
Date Tue, 04 Nov 2008 03:31:49 GMT
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.
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

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