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8307907: [ppc] Remove RTM locking implementation #14398

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TheRealMDoerr
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@TheRealMDoerr TheRealMDoerr commented Jun 9, 2023

This PR removes RTM code for PPC64. The instructions are not supported by Power10 processors.
The situation is even worse in Power9 compatibility mode on Power10. The VM detects RTM to be available, but the processor is unable to complete any transaction successfully.
The feature had so many problems and we never supported it in production.


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  • JDK-8307907: [ppc] Remove RTM locking implementation (Enhancement - P4)

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bridgekeeper bot commented Jun 9, 2023

👋 Welcome back mdoerr! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

@openjdk openjdk bot added the rfr Pull request is ready for review label Jun 9, 2023
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@TheRealMDoerr The following label will be automatically applied to this pull request:

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When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the hotspot hotspot-dev@openjdk.org label Jun 9, 2023
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mlbridge bot commented Jun 9, 2023

Webrevs

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@MBaesken MBaesken left a comment

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LGTM.
Maybe a release note would be nice because the change removed product flags.

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openjdk bot commented Jun 13, 2023

@TheRealMDoerr This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8307907: [ppc] Remove RTM locking implementation

Reviewed-by: mbaesken, rrich, stuefe

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At the time when this comment was updated there had been 72 new commits pushed to the master branch:

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➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

@openjdk openjdk bot added the ready Pull request is ready to be integrated label Jun 13, 2023
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TheRealMDoerr commented Jun 13, 2023

Thanks for the review! The flags were copied from x86, but they are officially only supported on x86: "Options related to RTM are available only for the Java HotSpot Server VM on x86 CPUs that support Transactional Synchronization Extensions (TSX)." [Java documentation]

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Looks good (except 2 nits). I'm glad we get rid of this complex code. Thanks!

@@ -2644,14 +2196,6 @@ void MacroAssembler::compiler_fast_lock_object(ConditionRegister flag, Register
bne(flag, failure);
}

#if INCLUDE_RTM_OPT
if (UseRTMForStackLocks && use_rtm) {
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Can RTM related method parameters (e.g. use_rtm) be removed?

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Good catch! There are even more parameters which are no longer needed. And I've found some more leftovers. I just removed all of them.

@@ -2769,19 +2300,6 @@ void MacroAssembler::compiler_fast_unlock_object(ConditionRegister flag, Registe
assert(LockingMode != LM_LIGHTWEIGHT || flag == CCR0, "bad condition register");
Label success, failure, object_has_monitor, notRecursive;

#if INCLUDE_RTM_OPT
if (UseRTMForStackLocks && use_rtm) {
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Can RTM related method parameters (e.g. use_rtm) be removed?

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Looks good!
Thanks, Richard.

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Thanks for the review!

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You also can probably remove transaction_failure_reason from assembler_ppc.hpp

} else {
throw e; // checking unsupported OS error is not necessary
}
throw e; // checking unsupported OS error is not necessary
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Why even catch this now?

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I think you can remove PPC_FEATURE2_HTM_NOSC too, right?

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@tstuefe: Thanks for reviewing! I've removed all you requested (and even more). I decided to remove the instruction emitters, too. We don't need them any more.

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This is a nice complexity reduction!

All good now.

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Thanks!
/integrate

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openjdk bot commented Jun 15, 2023

Going to push as commit de8aca2.
Since your change was applied there have been 74 commits pushed to the master branch:

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Jun 15, 2023
@openjdk openjdk bot closed this Jun 15, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jun 15, 2023
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openjdk bot commented Jun 15, 2023

@TheRealMDoerr Pushed as commit de8aca2.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

@TheRealMDoerr TheRealMDoerr deleted the 8307907_PPC64_remove_RTM branch June 15, 2023 09:53
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