What exactly does -XX:-TieredCompilation do?

Question

Using java -XX:+PrintFlagsFinal I found the TieredCompilation flag, and I read about it a bit online.

Yet, I still don\'t know exactly<

Answer 1

-XX:-TieredCompilation disables intermediate compilation tiers (1, 2, 3), so that a method is either interpreted or compiled at the maximum optimization level (C2).

As a side effect TieredCompilation flag also changes the number of compiler threads, the compilation policy and the default code cache size. Note that with TieredCompilation disabled

• there will be less compiler threads;
• simple compilation policy (based on method invocation and backedge counters) will be chosen instead of advanced compilation policy;
• default reserved code cache size will be 5 times smaller.

To disable C2 compiler and to leave only C1 with no extra overhead, set -XX:TieredStopAtLevel=1.

To disable all JIT compilers and to run everything in interpreter, use -Xint.