8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier #19278

kuaiwei · 2024-05-17T08:57:20Z

he origin patch for https://bugs.openjdk.org/browse/JDK-8324186 has 2 issues:
1 It show regression in some platform, like Apple silicon in mac os
2 Can not handle instruction sequence like "dmb.ishld; dmb.ishst; dmb.ishld; dmb.ishld"

It can be fixed by:
1 Enable AlwaysMergeDMB by default, only disable it in architecture we can see performance improvement (N1 or N2)
2 Check the special pattern and merge the subsequent dmb.

It also fix a bug when code buffer is expanding, st/ld/dmb can not be merged. I added unit tests for these.

This patch still has a unhandled case. Insts like "dmb.ishld; dmb.ishst; dmb.ish", it will merge the last 2 instructions and can not merge all three. Because when emitting dmb.ish, if merge all previous dmbs, the code buffer will shrink the size. I think it may break some resumption and think it's not a common pattern.

In previous PR #18467 , I tried an implementation to use state machine for merging. But it looks risky to pending instruction during emitting.

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Issue

JDK-8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier (Enhancement - P4)

Reviewers

Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 68c3018c
Andrew Haley (@theRealAph - Reviewer) ⚠️ Review applies to 68c3018c

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/19278/head:pull/19278
$ git checkout pull/19278

Update a local copy of the PR:
$ git checkout pull/19278
$ git pull https://git.openjdk.org/jdk.git pull/19278/head

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Checkout this PR locally:
$ git pr checkout 19278

View PR using the GUI difftool:
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https://git.openjdk.org/jdk/pull/19278.diff

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bridgekeeper · 2024-05-17T08:58:06Z

👋 Welcome back kuaiwei! 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 · 2024-05-17T08:58:53Z

@kuaiwei 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:

8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

Reviewed-by: shade, aph

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 48 new commits pushed to the master branch:

2a37764: 8333743: Change .jcheck/conf branches property to match valid branches
75dc2f8: 8330182: Start of release updates for JDK 24
054362a: 8332550: [macos] Voice Over: java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
9b436d0: 8333674: Disable CollectorPolicy.young_min_ergo_vm for PPC64
487c477: 8333647: C2 SuperWord: some additional PopulateIndex tests
d02cb74: 8333270: HandlersOnComplexResetUpdate and HandlersOnComplexUpdate tests fail with "Unexpected reference" if timeoutFactor is less than 1/3
02f2404: 8333560: -Xlint:restricted does not work with --release
606df44: 8332670: C1 clone intrinsic needs memory barriers
33fd6ae: 8333622: ubsan: relocInfo_x86.cpp:101:56: runtime error: pointer index expression with base (-1) overflowed
8de5d20: 8332865: ubsan: os::attempt_reserve_memory_between reports overflow
... and 38 more: https://git.openjdk.org/jdk/compare/d826127970bd2ae8bf4cacc3c55634dc5af307c4...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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@shipilev, @theRealAph) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

openjdk · 2024-05-17T08:59:24Z

@kuaiwei The following label will be automatically applied to this pull request:

hotspot

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.

mlbridge · 2024-05-17T09:02:12Z

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theRealAph · 2024-05-20T13:59:31Z

src/hotspot/cpu/aarch64/aarch64.ad


  ins_encode %{
    __ block_comment("membar_release");
-    __ membar(Assembler::LoadStore|Assembler::StoreStore);
+    __ membar(Assembler::StoreStore);


Do we need to respect AlwaysMergeDMBhere?

Yes, usually they can be merged in macroAssembler. but it can help to reduce the possibility of unmerged case. Thanks to point it.

I checked code again. They will be merged if enable AlwaysMergeDMB. So we can skip the check.

Add a comment:

// These will be merged if AlwaysMergeDMB is enabled.

Comment added.

shipilev

Cursory review:

shipilev · 2024-05-22T10:25:40Z

test/hotspot/gtest/aarch64/test_assembler_aarch64.cpp

+  asm_check((const unsigned int *)code.insts()->start(), insns, sizeof insns / sizeof insns[0]);
+}
+
+TEST_VM(AssemblerAArch64, merge_ldst) {


This test seems to be irrelevant for the issue at hand? Tests ld/st -> ldp/stp merging, not the barrier merges?

In this patch, I fixed an issue, dmb/st/ld may not merge if CodeBuffer is expanding, I added some unit tests to check it.

Aha. So the logic is that the same issue that affects dmb merging also affects ldp merging? All right, it's fine to leave it here then.

src/hotspot/cpu/aarch64/globals_aarch64.hpp

shipilev · 2024-05-22T11:07:57Z

test/hotspot/gtest/aarch64/test_assembler_aarch64.cpp

+  printf("%s\n", ss.as_string());
+}
+
+TEST_VM(AssemblerAArch64, merge_dmb) {


Given the previous experience with barrier merges that prompted the backout, I would prefer to have a more comprehensive test here, maybe an additional one. I am thinking something like the exhaustive combination of 4 back-to-back barriers of each of 5 types. This gives us 5^4 = 625 test cases, which I think is still manageable.

Test is added as merge_dmb_all_kinds

Right. I was implicitly thinking that we can do this without coding the explicit patterns into the test. As it stands now, it is hard to check that generated patterns are actually correct. Let me see if I can whip up a sample of what I had in mind.

I was thinking about this: improve-tests.patch. Note how it uses the constants for better readability, and also runs the test in both AlwaysMergeDMB modes. You might want to adapt other tests to similar pattern.

Thanks for your patch. I patched and add few sanity check.

theRealAph · 2024-05-29T11:11:35Z

This looks ready to me. I think we need jcstress with C1 and C2, and we should be done. @shipilev , do you agree?

shipilev · 2024-05-29T11:12:38Z

This looks ready to me. I think we need jcstress with C1 and C2, and we should be done. @shipilev , do you agree?

Yes. Just run jcstress with defaults, maybe limiting the time budget to about 24 hours, and we are done. Default configuration would work through different combinations of C1/C2 compilations for all actors, which is what we want to check for this change: that we don't mess up the barrier emitting scheme in different compilers/interpreters.

shipilev · 2024-05-29T11:34:09Z

Note that current jcstress run would likely fail due to JDK-8332670.

kuaiwei · 2024-05-30T08:24:55Z

This looks ready to me. I think we need jcstress with C1 and C2, and we should be done. @shipilev , do you agree?

Yes. Just run jcstress with defaults, maybe limiting the time budget to about 24 hours, and we are done. Default configuration would work through different combinations of C1/C2 compilations for all actors, which is what we want to check for this change: that we don't mess up the barrier emitting scheme in different compilers/interpreters.

I can run the jcstress test. I will run fastdebug build with
java -jar jcstress-latest.jar -tb 24h
Is it the correct command ?

shipilev · 2024-05-30T08:26:56Z

I can run the jcstress test. I will run fastdebug build with java -jar jcstress-latest.jar -tb 24h Is it the correct command ?

Yes, I think so.

shipilev · 2024-05-31T08:23:51Z

I can run the jcstress test. I will run fastdebug build with java -jar jcstress-latest.jar -tb 24h Is it the correct command >
Yes, I think so.

FTR, I ran Linux AArch64 server release on Graviton 3 instance (ergonomics selects -AlwaysMergeDMB there) for 12 hours. Apart from failures from JDK-8332670, I see no other trouble. Scheduled a quick run with +AlwaysMergeDMB as well.

kuaiwei · 2024-05-31T10:06:06Z

I can run the jcstress test. I will run fastdebug build with java -jar jcstress-latest.jar -tb 24h Is it the correct command >
Yes, I think so.

FTR, I ran Linux AArch64 server release on Graviton 3 instance (ergonomics selects -AlwaysMergeDMB there) for 12 hours. Apart from failures from JDK-8332670, I see no other trouble. Scheduled a quick run with +AlwaysMergeDMB as well.

Thanks for testing. I'm running jcstress on a neoverse-n2 instance. I got some "soft errs" in console output. Are they real error?

shipilev · 2024-05-31T10:08:47Z

test/hotspot/gtest/aarch64/test_assembler_aarch64.cpp

+constexpr uint32_t test_encode_dmb_ld = 0xd50339bf;
+constexpr uint32_t test_encode_dmb_st = 0xd5033abf;
+constexpr uint32_t test_encode_dmb    = 0xd5033bbf;


Can you maybe move these to the top, and use these constants across the test? You would not need the comments like 0xd5033abf, // dmb.ishst then.

shipilev · 2024-05-31T10:09:30Z

test/hotspot/gtest/aarch64/test_assembler_aarch64.cpp

+  asm_check((const unsigned int *)code.insts()->start(), insns, sizeof insns / sizeof insns[0]);
+}
+
+TEST_VM(AssemblerAArch64, merge_ldst) {


Aha. So the logic is that the same issue that affects dmb merging also affects ldp merging? All right, it's fine to leave it here then.

shipilev · 2024-05-31T11:02:31Z

src/hotspot/cpu/aarch64/macroAssembler_aarch64.hpp

@@ -150,6 +150,7 @@ class MacroAssembler: public Assembler {
  void bind(Label& L) {
    Assembler::bind(L);
    code()->clear_last_insn();
+    code()->set_last_label(pc());


OK, so we have added _last_label to shared code in codeBuffer, but only update it in aarch64. This would be surprising for other platforms. On the other hand, this is what we already do with _last_insn -- only implementing it for specific platforms. Probably fine, but it would be nice to strengthen this with asserts, maybe in separate PR.

It reminds me it could be applied to riscv. It also need merge membar. I will move this part to a new PR.

I need _last_label in this patch. I need it to check previous 2 instructions and they are not cross block boundary. I will create a new PR for RISCV only.

shipilev · 2024-05-31T11:04:49Z

Thanks for testing. I'm running jcstress on a neoverse-n2 instance. I got some "soft errs" in console output. Are they real error?

Soft errors are API inconsistencies that jcstress harness handled. As long as you don't have new hard errors, you are fine.

kuaiwei · 2024-06-03T06:42:18Z

I can run the jcstress test. I will run fastdebug build with java -jar jcstress-latest.jar -tb 24h Is it the correct command >
Yes, I think so.

FTR, I ran Linux AArch64 server release on Graviton 3 instance (ergonomics selects -AlwaysMergeDMB there) for 12 hours. Apart from failures from JDK-8332670, I see no other trouble. Scheduled a quick run with +AlwaysMergeDMB as well.

Thanks for testing. I'm running jcstress on a neoverse-n2 instance. I got some "soft errs" in console output. Are they real error?

My jcstress test is done and no error is reported.

theRealAph

I think we're done here. Thank you for your patience and hard work.
@shipilev, are you happy too?

shipilev

Yes, I believe we are done. Good job!

kuaiwei · 2024-06-04T02:12:59Z

Thanks for your review.

kuaiwei · 2024-06-04T02:13:11Z

/integrate

openjdk · 2024-06-04T02:13:36Z

@kuaiwei
Your change (at version 68c3018) is now ready to be sponsored by a Committer.

kuaiwei · 2024-06-04T11:00:42Z

@theRealAph @shipilev Could you help sponsor it ?
Thanks.

shipilev · 2024-06-04T17:04:19Z

GH says the branch has conflicts that must be resolved. Merging from master is advisable anyway to avoid merge surprises. Let's do that before integrating.

TobiHartmann · 2024-06-05T05:18:22Z

Given that the first version of the patch had some issues, I would recommend waiting for the fork tomorrow and only integrating this into JDK 24.

TobiHartmann · 2024-06-05T05:19:55Z

I'll run this through our correctness and performance testing and report back once it passed.

shipilev · 2024-06-07T09:06:12Z

I'll run this through our correctness and performance testing and report back once it passed.

How was it, Tobias? Any surprises?

8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

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openjdk bot added the rfr Pull request is ready for review label May 17, 2024

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Make MacroAssembler::merge more clear

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kuaiwei added 2 commits May 23, 2024 13:46

Add more unit tests

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Refine merge dmb test cases

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Add comment in aarch64.ad

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Use constexpr for test encoding

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8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier #19278

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8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier #19278

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kuaiwei commented May 17, 2024 • edited by openjdk bot

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