JDK-8328986 : Deprecate UseRTM* flags for removal
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 23
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • OS: generic
  • CPU: x86
  • Submitted: 2024-03-25
  • Updated: 2024-03-28
  • Resolved: 2024-03-27
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JDK 23
23 b16Fixed
Related Reports
CSR :  
JDK-8328991 - Deprecate UseRTM* flags for removal
Relates :  
JDK-8031320 - Use Intel RTM instructions for locks
Relates :  
JDK-8320321 - RTM locking not supported for LM_LIGHTWEIGHT
Relates :  
JDK-8292082 - Deprecate UseRTM* for removal
Relates :  
JDK-8329141 - Obsolete RTM flags and code
Description
HotSpot supports RTM (restricted transactional memory) to be used for locking since JDK 8 on Intel's CPU (JDK-8031320). It was added to other platforms but has since been disabled and removed on all but Intel processors. There was attempt to deprecate it (JDK-8292082) during JDK 20 development but at that time it was decided to keep it. Recently we discussed this with Intel and they agreed with RTM deprecation and removal from HotSpot.

RTM adds unnecessarily to complexity and maintenance burden. It was never enabled by default because it only helped with some heavy lock contentions. Additionally new LIGHTWEIGHT locking implementation will not support it: JDK-8320321.

I propose to deprecate the related flags and remove the flags and all related code in a later release according to process.
Comments
Changeset: 3eb1d05d Author: Vladimir Kozlov <kvn@openjdk.org> Date: 2024-03-27 21:56:53 +0000 URL: https://git.openjdk.org/jdk/commit/3eb1d05d853e92949bf239ac4b88436a4fe0997d
27-03-2024
A pull request was submitted for review. URL: https://git.openjdk.org/jdk/pull/18478 Date: 2024-03-25 20:41:20 +0000
25-03-2024
We are not testing RTM feature since JDK 14: JDK-8226899.
25-03-2024
Note, from 11 RTM related flags only 3 are product flags, there rest are experimental flags.
25-03-2024