8227060: Optimize safepoint cleanup subtask order #9515

coleenp · 2022-07-15T12:36:27Z

Most of the analysis in the CR is for code that's removed, but I found one safepoint cleanup task that's unused. Also the dictionary resizing and symbol/string table rehashing, while rare, could take a long time so I moved them sooner in the list.
Tested with tier1-3.

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-8227060: Optimize safepoint cleanup subtask order

Reviewers

Kim Barrett (@kimbarrett - Reviewer)
Patricio Chilano Mateo (@pchilano - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/9515/head:pull/9515
$ git checkout pull/9515

Update a local copy of the PR:
$ git checkout pull/9515
$ git pull https://git.openjdk.org/jdk pull/9515/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 9515

View PR using the GUI difftool:
$ git pr show -t 9515

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/9515.diff

bridgekeeper · 2022-07-15T12:38:21Z

👋 Welcome back coleenp! 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 · 2022-07-15T12:41:05Z

@coleenp 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 · 2022-07-15T12:45:39Z

Webrevs

kimbarrett

A bit of history here. It seems that some of the point of the original CR has
disappeared. There used to be a use of parallel_java_threads_do at the start
(from JDK-8180932), with the CR suggesting moving that to the end. That
disappeared with JDK-8246476. So some of the point of the CR has gone away.
But ordering the remaining tasks from expensive to cheap is still sensible,
and the new order mostly [*] looks plausible.

A different (pre-existing) problem is that the use of the workers isn't great.
The amount of parallelism is just the workgang's current active_workers(),
with no regard to how much parallelism we have. Presently the maximum useful
amount of parallelism is the number of subtasks, so 6 (which might easily and
likely be reduced with some pre-checks). So we're going to apply
active_workers threads (whatever that happens to be at the moment) to a task
which can use only a relatively small and fixed [*] number of threads.
Improving the use of the workgang should be a separate RFE.

[*] JDK-8253180 later (after JDK-8246476) introduced the serial threads_do to
set GC watermarks. Digging into it a bit, that doesn't look obviously
lightweight; I wonder if it should be (should have been) parallelized (and
placed at the end of the work). But that's a separate RFE.

kimbarrett · 2022-07-16T00:15:11Z

src/hotspot/share/runtime/safepoint.cpp

-};
-
-class ParallelSPCleanupTask : public WorkerTask {
+class ParallelCleanupTask : public WorkerTask {
 private:
  SubTasksDone _subtasks;
  uint _num_workers;


[pre-existing] _num_workers seems to no longer be used.

kimbarrett · 2022-07-16T00:20:57Z

src/hotspot/share/runtime/safepoint.cpp

@@ -547,33 +538,23 @@ class ParallelSPCleanupTask : public WorkerTask {
    }
  };

+  class SafepointCleanupThreadClosure : public ThreadClosure {


The new name doesn't seem to have much more to do with what it does than did the old name. The class definition could be moved to the single point of use and just called "Closure" to avoid needing to come up with a good name :)

coleenp · 2022-07-16T15:23:19Z

@kimbarrett I made your suggested improvements, even though a class in the middle of function looks odd to me. Maybe someday it can be replaced with a lambda. Reran tier1 tests locally. I agree that the problem that this was supposed to solve may be gone now, but if we do resizing and rehashing, it would be good to have that in parallel with the other tasks. The threads are already created, otherwise the cost of creating them would not be worth making this parallel. I can't comment on how much work the lazy stack watermark processing is.

kimbarrett

Looks good. There may be a couple of followup RFEs to be filed; we can discuss those later.

openjdk · 2022-07-17T18:37:08Z

@coleenp 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:

8227060: Optimize safepoint cleanup subtask order

Reviewed-by: kbarrett, pchilanomate

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 44 new commits pushed to the master branch:

bbc5748: 8272096: Exceptions::new_exception can return wrong exception
a41b12f: 8290512: G1: Fix typo in allocation statistics log message
e02627c: 8290397: LoadLibraryUnload.java failed with "Too few cleared WeakReferences"
2ff2208: 8289804: Remove redundant stream() call before forEach in jdk.jshell
f5a7de8: 8290379: Parse error with parenthesized pattern and guard using an array
612d8c6: 8290456: remove os::print_statistics()
d7f0de2: 8290460: Alpine: disable some panama tests that rely on std::thread
dfbc691: 8289524: Add JFR JIT restart event
4e6cd67: 8290000: Bump macOS GitHub actions to macOS 11
af86cd3: 8290463: Fix several comment typos in sun.security.ec
... and 34 more: https://git.openjdk.org/jdk/compare/3ad39505605f8eab74adec9c68f211dd44796759...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.

pchilano

Looks good to me.

coleenp · 2022-07-19T16:29:57Z

Thank you, Kim and Patricio!
/integrate

openjdk · 2022-07-19T16:32:20Z

Going to push as commit 96a542f.
Since your change was applied there have been 45 commits pushed to the master branch:

2cb659e: 8290391: Reduce runtime of java.util package microbenchmarks
bbc5748: 8272096: Exceptions::new_exception can return wrong exception
a41b12f: 8290512: G1: Fix typo in allocation statistics log message
e02627c: 8290397: LoadLibraryUnload.java failed with "Too few cleared WeakReferences"
2ff2208: 8289804: Remove redundant stream() call before forEach in jdk.jshell
f5a7de8: 8290379: Parse error with parenthesized pattern and guard using an array
612d8c6: 8290456: remove os::print_statistics()
d7f0de2: 8290460: Alpine: disable some panama tests that rely on std::thread
dfbc691: 8289524: Add JFR JIT restart event
4e6cd67: 8290000: Bump macOS GitHub actions to macOS 11
... and 35 more: https://git.openjdk.org/jdk/compare/3ad39505605f8eab74adec9c68f211dd44796759...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-07-19T16:32:39Z

@coleenp Pushed as commit 96a542f.

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

8227060: Optimize safepoint cleanup subtask order

6e5786c

openjdk bot added the rfr Pull request is ready for review label Jul 15, 2022

openjdk bot added the hotspot hotspot-dev@openjdk.org label Jul 15, 2022

Kim's improvement ideas.

9e49a30

kimbarrett reviewed Jul 16, 2022

View reviewed changes

More Kim improvements.

c47551f

kimbarrett approved these changes Jul 17, 2022

View reviewed changes

openjdk bot added the ready Pull request is ready to be integrated label Jul 17, 2022

pchilano approved these changes Jul 19, 2022

View reviewed changes

openjdk bot added the integrated Pull request has been integrated label Jul 19, 2022

openjdk bot closed this Jul 19, 2022

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jul 19, 2022

coleenp deleted the safepoint branch July 19, 2022 16:33

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

8227060: Optimize safepoint cleanup subtask order #9515

8227060: Optimize safepoint cleanup subtask order #9515

coleenp commented Jul 15, 2022 •

edited by openjdk bot

Loading

bridgekeeper bot commented Jul 15, 2022

openjdk bot commented Jul 15, 2022

mlbridge bot commented Jul 15, 2022 •

edited

Loading

kimbarrett left a comment

kimbarrett Jul 16, 2022

kimbarrett Jul 16, 2022

coleenp commented Jul 16, 2022

kimbarrett left a comment

openjdk bot commented Jul 17, 2022 •

edited

Loading

pchilano left a comment

coleenp commented Jul 19, 2022

openjdk bot commented Jul 19, 2022

openjdk bot commented Jul 19, 2022

8227060: Optimize safepoint cleanup subtask order #9515

8227060: Optimize safepoint cleanup subtask order #9515

Conversation

coleenp commented Jul 15, 2022 • edited by openjdk bot Loading

Progress

Issue

Reviewers

Reviewing

bridgekeeper bot commented Jul 15, 2022

openjdk bot commented Jul 15, 2022

mlbridge bot commented Jul 15, 2022 • edited Loading

Webrevs

kimbarrett left a comment

Choose a reason for hiding this comment

kimbarrett Jul 16, 2022

Choose a reason for hiding this comment

kimbarrett Jul 16, 2022

Choose a reason for hiding this comment

coleenp commented Jul 16, 2022

kimbarrett left a comment

Choose a reason for hiding this comment

openjdk bot commented Jul 17, 2022 • edited Loading

pchilano left a comment

Choose a reason for hiding this comment

coleenp commented Jul 19, 2022

openjdk bot commented Jul 19, 2022

openjdk bot commented Jul 19, 2022

coleenp commented Jul 15, 2022 •

edited by openjdk bot

Loading

mlbridge bot commented Jul 15, 2022 •

edited

Loading

openjdk bot commented Jul 17, 2022 •

edited

Loading