8261496: Shenandoah: reconsider pacing updates memory ordering

[shipilev]

Shenandoah pacer uses atomic operations to update budget, progress, allocations seen. Hotspot's default for atomic operations is memory_order_conservative, which emits two-way memory fences around the CASes at least on AArch64 and PPC64.

This is excessive for pacing, as we do not piggyback memory effects on it. All pacing updates can use "relaxed".

Additional testing:

• Linux x86_64 hotspot_gc_shenandoah
• Linux AArch64 hotspot_gc_shenandoah
• Linux AArch64 tier1 with Shenandoah

---

Progress

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Issue

• JDK-8261496: Shenandoah: reconsider pacing updates memory ordering

Reviewers

• Zhengyu Gu (@zhengyu123 - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/2501/head:pull/2501
$ git checkout pull/2501

[bridgekeeper]

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[openjdk]

@shipilev The following labels will be automatically applied to this pull request:

• hotspot-gc
• shenandoah

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[mlbridge]

Webrevs

• 00: Full (67fb955)

[zhengyu123]

Looks good to me

[openjdk]

@shipilev 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:

8261496: Shenandoah: reconsider pacing updates memory ordering

Reviewed-by: zgu

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 23 new commits pushed to the master branch:

• a772639: 8261298: LinuxPackage.c, getJvmLauncherLibPath RPM->DEB typo
• 52fc01b: 8261268: LOAD_INSTANCE placeholders unneeded for parallelCapable class loaders
• a3d6e37: 8261302: NMT: Improve malloc site table hashing
• ad54d8d: 8260934: java/lang/StringBuilder/HugeCapacity.java fails without Compact Strings
• 752f92b: 6211242: AreaAveragingScaleFilter(int, int): IAE is not specified
• 3af334a: 6211257: BasicStroke.createStrokedShape(Shape): NPE is not specified
• 4619f37: 8261472: BasicConstraintsExtension::toString shows "PathLen:2147483647" if there is no pathLenConstraint
• 699a3cd: 8223188: Removed unnecessary #ifdef __cplusplus from .cpp sources
• 05c6009: 8259656: fixpath.sh changes broke _NT_SYMBOL_PATH in RunTests.gmk
• ef7ee3f: 8225081: Remove Telia Company CA certificate expiring in April 2021
• ... and 13 more: https://git.openjdk.java.net/jdk/compare/5183d8ae1eec86202eace2c4770f81edbc73cb68...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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

[shipilev]

/integrate

[openjdk]

@shipilev Since your change was applied there have been 77 commits pushed to the master branch:

• 7c93159: 8261503: Shenandoah: reconsider verifier memory ordering
• d9744f6: 8261608: Move common CDS archive building code to archiveBuilder.cpp
• 235da6a: 8261672: Reduce inclusion of classLoaderData.hpp
• 95d7312: 8261585: Restore HandleArea used in Deoptimization::uncommon_trap
• 849390a: 8260401: StackOverflowError on open WindowsPreferences
• 735757f: 8261661: gc/stress/TestReclaimStringsLeaksMemory.java fails because Reserved memory size is too big
• e29c560: 8247514: Improve clhsdb 'findpc' ability to determine what an address points to by improving PointerFinder and PointerLocation classes
• dc46aa8: 8261534: Test sun/security/pkcs11/KeyAgreement/IllegalPackageAccess.java fails on platforms where no nsslib artifacts are defined
• f0d9829: 8261533: Java_sun_font_CFont_getCascadeList leaks memory according to Xcode
• 06170b7: 8261662: Rename compute_loader_lock_object
• ... and 67 more: https://git.openjdk.java.net/jdk/compare/5183d8ae1eec86202eace2c4770f81edbc73cb68...master

Your commit was automatically rebased without conflicts.

Pushed as commit 4642730.

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