RFR: 8290344: Start/stop displaysync affects performance in metal rendering pipeline [v2]

[Alexey Ushakov]

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> Stopping DisplayLink once we are done with blitting was used to fix https://bugs.openjdk.org/browse/JDK-8259038 . I think with displayLink active count as 4 we might see unnecessary(~4) displayLink callbacks when we just draw text and leave it as noticed in the bug.  But i think this tradeoff is fine as we are trying to achieve balance between power and performance.
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> Also this change should not cause state management issues as we are just maintaining displayLink for longer time. @avu Could you please verify that we are not seeing issues like https://bugs.openjdk.org/browse/JDK-8247332 ?

I’ve checked the scenario from JDK-8247332 - everything works as expected.

Best Regards,
Alexey

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> PR: https://git.openjdk.org/jdk/pull/9512