JIT compiler - compiler choosing options

Question

On 64 bit linux, with java8, when running java command, it seems all the 3 options -client / -server / -d64 are using the 64-bit server compiler.

The questions are: (for 64bit linux with java8)

• Since -client and -server use the same compiler, does it makes any difference to specify one of the 2 options?
• For a long running java daemon program, is it preferred to use -server together with -XX:+TieredCompilation or without it, when during the startup time it's ok to be a little slow.

Answer 1

Look at the file jre/lib/amd64/jvm.cfg. You'll likely see the lines

-server KNOWN
-client IGNORE

This means that -client option is ignored. -server also does nothing, since JDK 8 for x64 has only one JVM that includes both C1 and C2 compilers, and the tiered compilation is on by default.

with -XX:+TieredCompilation or without it

Does not matter, because this option is on by default. The advanced compilation policy works fine for both client-grade and server-grade applications. There is no usually need to turn it off manually.