8366441: AArch64: Support WFET in OnSpinWait

[ruben-arm]

Implement OnSpinWait based on WFET - wait for event with timeout:

• introduce OnSpinWaitDelay - the OnSpinWait time in nanoseconds;
• the OnSpinWaitInstCount is expected to be 1 when WFET is used;
• the waiting loop is followed by SB - to ensure following instructions aren't speculated until wait is finished;
• the timer register is read via the self-synchronized view CNTVCTSS_EL0 to prevent the read being hoisted out of the loop.

The WFET and CNTVCTSS_EL0 read are added to aarch64-asmtest.py as hex values - using the instruction mnemonics would require support of -march=armv9-2.a, and consequently, the binutils 2.36+.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8366441: AArch64: Support WFET in OnSpinWait (Enhancement - P4)

Contributors

• Stuart Monteith <[email protected]>

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/27030/head:pull/27030
$ git checkout pull/27030

Update a local copy of the PR:
$ git checkout pull/27030
$ git pull https://git.openjdk.org/jdk.git pull/27030/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 27030

View PR using the GUI difftool:
$ git pr show -t 27030

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/27030.diff

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[ruben-arm]

/contributor add @stooart-mon

[openjdk]

@ruben-arm
Contributor Stuart Monteith <[email protected]> successfully added.

[theRealAph]

The WFET and CNTVCTSS_EL0 read are added to aarch64-asmtest.py as hex values - using the instruction mnemonics would require support of -march=armv9-2.a, and consequently, the binutils 2.36+.

So please use binutils 2.36+.

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[ruben-arm]

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[openjdk]

@ruben-arm this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout pr-8366441
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push