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From "Xiao-Feng Li" <xiaofeng...@gmail.com>
Subject Re: [performance] Startup cost is high for Harmony (HARMONY-6002)
Date Wed, 12 Nov 2008 09:36:45 GMT
On Wed, Nov 12, 2008 at 4:25 PM, Regis <xu.regis@gmail.com> wrote:
> Wenlong Li wrote:
>> Regis,
>> Sorry for late response. The class preload and initialization happens
>> in vm_init.cpp, and totally around 270 classes are preloaded before
>> executing main() method.
>> We can pack preloaded classes in one jar, and leave other jars there.
>> The question is when requesting a new class, how do determine which
>> jar has it? In current implementation, we have to parse all jars to
> Harmony modules division is based on the java package, so maybe a index
> could help this. for example, we could index all the package names begin
> whith java/javax/o.a.h and the bootstrap jar files, so we can quickly find
> which jar we should looking for.
>> load this class. That means, opening and closing all jars in classpath
>> is still unavoidable, and this time happens in running user code. In
>> contrast, the RI packs most classes in rt.jar, and totally four jars
>> are provided. I suppose RI also parses all classes in these four jars,
>> and read them into memory. Later when a class is reqired, a service of
>> providing class is made by looking up the pre-loaded classes in
>> memory.
>> In Harmony, it just parses all jars (totall more than 40) in
>> classpath, and reads all classes in these jars into memory. Later on
>> accessing a class, this data structure is scaned to define the
>> requested class. So current implementation is loading on-demand, but
>> has too many files to parse.
> we parse all jars, but most of them may never be used. That would be great
> if we could parsing jars on-demand. And a another thought is, as you said,
> if remove some jars from bootstrap classpath, the startup time improve
> obviously, so is it possible to provide a vm option, like -Xpreload, to
> specify which boots jars should be parsed during startup time? And this
> option could not only speed the jvm startup, but also reduce the memory
> footprint.

It is a good idea to introduce an option.


>> Any comment?
>> Thx, Wenlong
>> On Tue, Nov 4, 2008 at 12:46 PM, Regis <xu.regis@gmail.com> wrote:
>>> 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


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