RFR: Unconditional conditional card marking

[Y. Srinivas Ramakrishna]

On Fri, 21 Apr 2023 15:32:43 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> For the overwhelming majority of current systems, it makes little sense to run without conditional card marks enabled. G1, for example, makes its card marks unconditional. In other words, G1 does not respond to `UseCondCardMark`. This also simplifies code, eliminates one additional testing configuration, and provides safety for the cases where `UseCondCardMark` is accidentally disabled.
> 
> Additional testing: 
>  - [x] macos-aarch64-server-fastdebug, `hotspot_gc_shenandoah`

Changes look good.

Historically, however, conditional card marks were found to reduce performance, but may be there is newer data that shows that it's better to use conditional card marks to reduce cache coherency traffic as the core counts and cache sizes have both gone up?

Can we collect some fresh relative performance numbers?

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Marked as reviewed by ysr (Author).

PR Review: https://git.openjdk.org/shenandoah/pull/264#pullrequestreview-1396231313