Currently ShenandoahPacing is enabled by default, https://github.com/openjdk/jdk/blob/969c2af95387992c55a2e1768de848a354e74127/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp#L230

We notice it has a noticeable impact on long tail latency and there is a bug(https://bugs.openjdk.org/browse/JDK-8340490) created to improve it.

In the internal release, we have disabled it by default, so far there is no known impact with it disabled, we think it might be fine to disable it in upstream.

(May need to convert CSR with more details since it changes the default value of command line option `ShenandoahPacing`)