RFR: 8325872: Make GuaranteedSafepointInterval default 0

[Erik Österlund]

On Wed, 17 Apr 2024 16:03:57 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This change keeps the GuaranteedSafepointInterval option for use with -XX:+HandshakeALot and -XX:+SafepointALot and removes it from working with the MonitorDeflationThread.  The MonitorDeflation thread has it's own timers and doesn't require safepoint to trigger anymore, so the GuaranteedSafepointInterval is logically unrelated except for historical reasons.
> The option AsyncDeflationInterval default is 250 so was used anyway in this code for the monitor deflation thread timer.
> 
> Tested with tier1-8.  Also performance tested this which didn't show any improvements.

Changes requested by eosterlund (Reviewer).

src/hotspot/share/runtime/arguments.cpp line 3649:

> 3647: 
> 3648:   // The VMThread needs to stop now and then to execute these debug options.
> 3649:   if (HandshakeALot && SafepointALot && FLAG_IS_DEFAULT(GuaranteedSafepointInterval)) {

Should this be (HandshakeALot || SafepointALot) instead of HandshakeALot && SafepointALot?

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PR Review: https://git.openjdk.org/jdk/pull/18820#pullrequestreview-2006506171
PR Review Comment: https://git.openjdk.org/jdk/pull/18820#discussion_r1569120339