RFR: 8255047: Add HotSpot flag to use with debuggers that restrict the CPU…

[Stefan Karlsson]

On Wed, 21 Oct 2020 07:24:52 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Perhaps: `UseDebuggerErgo` for the main option name with
>> `UseDebuggerErgo1` ... `UseDebuggerErgoN` for the suboptions
>> where `UseDebuggerErgo` enables all the numbered
>> `UseDebuggerErgo<X>` options in one go.
>> 
>> Update: Yes, this is the way that I have always wished that
>> `UseNewCode*` worked.
>
> @dcubed-ojdk Thanks for the suggestion. I like it.

I've updated the patch with the suggestion from Dan. The flags now work as follows:
-XX:+UseDebuggerErgo turns on all ergonomics / workarounds
-XX:-/+UseDebuggerErgo1 fixes processor id vs processor count problems
-XX:-/+UseDebuggerErgo2 limits the number of JVM threads and turns of NUMA

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PR: https://git.openjdk.java.net/jdk/pull/763