RFR: 8318986: Improve GenericWaitBarrier performance [v4]

[Robbin Ehn]

On Tue, 7 Nov 2023 20:18:11 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/share/utilities/waitBarrier_generic.hpp line 38:
>> 
>>> 36:   private:
>>> 37:     DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0);
>>> 38: 
>> 
>> Just reading the padding, it's unclear why the two pads are where they are.
>> Can you add a comment about why choose these two locations?
>
> Wanted to make sure nothing interferes with cells. But now I realize we actually overpad between the cells (due to both pre-cell and post-cell padding), and underpad for the barrier itself! Fixed in new commit.

Ok!

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PR Review Comment: https://git.openjdk.org/jdk/pull/16404#discussion_r1386104404