如何加速 JVM？

Question

I'm writing some java software that is being run on both Linux and Windows XP Embedded on a Vortex86 Chip. The software usually loads in 2-3 seconds in Windows XP but when I try and load it in Linux it takes around 10-12 seconds. I don't think its a code optimization issue because it takes 1 second to run a Hello World program.

Any suggestions would be greatly appreciated. Pre-loading java is an option because the machine will only be running these programs but I have no idea how to do that.

Answer 1

As Matt pointed out, there are many factors at play. With your incomplete description, it's impossible to make targeted recommendations. Having said that, here are a few things to try:

• Profile your memory utilization with -verbose:gc and increase the memory allotted to your program (java -Xms512m -Xmx512m)
• Check that the version of Java on both machines is roughly equivalent
• Check that the hardware on both machines is roughly equivalent
• Check whether both machines are quiet when you're measuring performance
• Make sure both are running in either 32-bit or 64-bit, and you're not reporting results from a mixed profile.
• Check for startup scripts that your program may be using for one platform, but may be missing for the other (eg a run.properties)

Answer 2

If you have run Java before, the shared files and rt.jar will be in memory. ie pre-loaded for you. I can only imagine your Linux machine is very low on memory and it has to load everything from disk each time.

On my Linux box

$ time java -cp . HelloWorld
Hello World.

real     0m0.043s
user     0m0.030s
sys      0m0.010s

The total time to start and run is 0.043 seconds. Can you do a similar test with your hello world?