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Java G1 Tuning Impacts - Multiple JVMs on Host

User_U6GUEAug 19 2021

I'm helping tune a Mule based app with a 12 GB heap and need to switch from the CMS to G1 garbage collection policy. The RHEL host in question has 12 logical processors and is hosting 3 Oracle JVM running Mule based app.
The calculation for the ParallelGCThreads is straightforward (5/8) * 12 = 7.5 rounded up to 8.
My question: does that calculation need to be adjusted because there are 3 JVMs? Do the 3 competing Oracle 1.8 JVMs compel me to reduce that logical CPU number to 4 in order to treat each as using 1/3 of the available logical CPUs??
Want to start this tuning exercise off on the right foot.

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Added on Aug 19 2021