RFR: 8307766: Linux: Provide the option to override the timer slack [v7]

[Aleksey Shipilev]

On Mon, 3 Jul 2023 08:04:05 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> We only call pctrl if the flag is >0. So, 0 has already the meaning of "ignore".
>
> That seems a bug then. We should pass zero to pctrl if that is the value set (even if the current implementation does nothing for a value of zero).

Right. Thinking more about it, I think I am going to use `-1` to mean that all new paths are completely disabled, so that we don't call `prctl` by default, and do not print the slack values at all. With `0`, we rely on system default, and then print out the actual values. With `> 0`, we both override the value and print the current slack values.

This insulates current code from this experimental addition better.

See new commits.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13889#discussion_r1252949372