-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.