Java SE supports an option called "interpreted mode" that disables the JIT. It is enabled by passing the -Xint argument when launching the VM. One reason for enabling this option is to reduce the performance jitter caused by just-in-time compilation.
The Sun Java RTS apparently supports this option as well. At least, it doesn't complain when I use it. Does it in fact work? That is, does -Xint actually disable the JIT and make RTS performance more predictable?
Yes Java RTS supports -Xint just as Java SE does. This improves predictability in the sense that you won't get unpredictable JIT compilation occurring, but it doesn't mean that interpreted execution is necessarily predictable in itself.
Interpreted execution is also very slow. If you want performance and predictability then use the Initialization Time Compilation (ITC) feature of Java RTS.