RFR: 8319048: Monitor deflation unlink phase prolongs time to safepoint [v8]

[Aleksey Shipilev]

On Mon, 20 Nov 2023 22:21:56 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 15 additional commits since the last revision:
>> 
>>  - No need for vm.flagless
>>  - Use precise deflated_count
>>  - Rework option handling
>>  - Merge branch 'master' into JDK-8319048-monitor-deflation-unlink
>>  - Merge branch 'master' into JDK-8319048-monitor-deflation-unlink
>>  - Merge branch 'master' into JDK-8319048-monitor-deflation-unlink
>>  - Move unlink_batch init to proper place
>>  - Add invariant checking
>>  - Merge branch 'master' into JDK-8319048-monitor-deflation-unlink
>>  - Fix test after recent test infra renames
>>  - ... and 5 more: https://git.openjdk.org/jdk/compare/36ae7822...5c41e46e
>
> src/hotspot/share/runtime/synchronizer.cpp line 127:
> 
>> 125:       // Unlink the found batch.
>> 126:       if (prev == nullptr) {
>> 127:         // The batch is not preceded by another monitor. There is a chance the batch starts at head.
> 
> Perhaps:
> // The current batch is the first batch so there is a chance that it starts at head.

Updated.

> src/hotspot/share/runtime/synchronizer.cpp line 135:
> 
>> 133:             prev = n;
>> 134:           }
>> 135:           assert(prev != nullptr, "Should have found the batch head");
> 
> Perhaps:
> "Should have found the prev for the current batch"

Right, fixed.

> src/hotspot/share/runtime/synchronizer.cpp line 140:
> 
>> 138:       } else {
>> 139:         // The batch is preceded by another monitor. This guarantees the current batch does not
>> 140:         // start at head. Remove the entire batch without updating the head.
> 
> Perhaps
> 
> // The current batch is preceded by another batch. This guarantees the current batch
> // does not start at head. Unlink the entire current batch without updating the head.

Fixed.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/16412#discussion_r1400362449
PR Review Comment: https://git.openjdk.org/jdk/pull/16412#discussion_r1400362895
PR Review Comment: https://git.openjdk.org/jdk/pull/16412#discussion_r1400363755