RFR: 8343704: Bad GC parallelism with processing Cleaner queues

[Aleksey Shipilev]

On Tue, 12 Nov 2024 16:00:39 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See the bug for more discussion and reproducer. This PR replaces the linked list with an `ArrayList` wrapper that manages synchronization, search and replacements effectively. There are possible improvements here, most glaring is parallelism that is currently knee-capped by global synchronization. The synchronization scheme follows what we already have, and I think it is safer to continue with it right now.
> 
> I'll put performance data in a separate comment.
> 
> Additional testing:
>  - [x] Original reproducer improves drastically
>  - [x] New microbenchmark shows no regression on "churning" tests, which covers insertion/removal perf
>  - [x] New microbenchmark shows improvement on Full GC times (crude, but repeatable), serves as a proxy for reproducer
>  - [x] `java/lang/ref` tests in release 
>  - [ ] `all` tests in fastdebug

Original reproducer on my M1:


# Before
...
[8.989s][info ][gc       ] GC(50) Pause Young (Normal) (G1 Evacuation Pause) 608M->21M(1011M) 46.562ms
[9.187s][info ][gc       ] GC(51) Pause Young (Normal) (G1 Evacuation Pause) 608M->22M(1011M) 45.286ms
[9.387s][info ][gc       ] GC(52) Pause Young (Normal) (G1 Evacuation Pause) 609M->21M(1011M) 45.636ms
[9.592s][info ][gc       ] GC(53) Pause Young (Normal) (G1 Evacuation Pause) 608M->22M(1015M) 47.514ms
[9.794s][info ][gc       ] GC(54) Pause Young (Normal) (G1 Evacuation Pause) 612M->22M(1015M) 46.807ms
[9.993s][info ][gc       ] GC(55) Pause Young (Normal) (G1 Evacuation Pause) 612M->21M(1015M) 45.964ms

# After
...
[6.964s][info ][gc       ] GC(50) Pause Young (Normal) (G1 Evacuation Pause) 521M->36M(830M) 11.096ms
[7.108s][info ][gc       ] GC(51) Pause Young (Normal) (G1 Evacuation Pause) 521M->36M(830M) 11.380ms
[7.252s][info ][gc       ] GC(52) Pause Young (Normal) (G1 Evacuation Pause) 521M->36M(830M) 11.293ms
[7.397s][info ][gc       ] GC(53) Pause Young (Normal) (G1 Evacuation Pause) 520M->35M(830M) 12.407ms
[7.540s][info ][gc       ] GC(54) Pause Young (Normal) (G1 Evacuation Pause) 520M->37M(830M) 11.096ms


A closest reproducer in form of JMH test also improves:


Benchmark          (count)  (recipFreq)  Mode  Cnt   Score    Error  Units

# Before
CleanerGC.test       16384          N/A  avgt   15   2.170 ±  0.082  ms/op
CleanerGC.test       65536          N/A  avgt   15   2.281 ±  0.104  ms/op
CleanerGC.test      262144          N/A  avgt   15   6.176 ±  0.466  ms/op
CleanerGC.test     1048576          N/A  avgt   15  22.913 ±  5.171  ms/op
CleanerGC.test     4194304          N/A  avgt   15  77.781 ± 14.937  ms/op

# After
CleanerGC.test       16384          N/A  avgt   15   2.169 ± 0.061  ms/op
CleanerGC.test       65536          N/A  avgt   15   2.247 ± 0.083  ms/op
CleanerGC.test      262144          N/A  avgt   15   3.822 ± 0.191  ms/op
CleanerGC.test     1048576          N/A  avgt   15   9.750 ± 0.638  ms/op
CleanerGC.test     4194304          N/A  avgt   15  33.842 ± 5.382  ms/op


Churn benchmark, which covers insertion/removal perf, matches the original implementation closely:


Benchmark          (count)  (recipFreq)  Mode  Cnt   Score    Error  Units

# Before
CleanerChurn.test      N/A          128  avgt    9   7.063 ±  0.262  ns/op
CleanerChurn.test      N/A          256  avgt    9   5.669 ±  0.118  ns/op
CleanerChurn.test      N/A          512  avgt    9   5.025 ±  0.066  ns/op
CleanerChurn.test      N/A         1024  avgt    9   4.714 ±  0.086  ns/op
CleanerChurn.test      N/A         2048  avgt    9   4.595 ±  0.091  ns/op

# After
CleanerChurn.test      N/A          128  avgt    9   7.050 ± 0.847  ns/op
CleanerChurn.test      N/A          256  avgt    9   5.378 ± 0.186  ns/op
CleanerChurn.test      N/A          512  avgt    9   4.896 ± 0.112  ns/op
CleanerChurn.test      N/A         1024  avgt    9   4.712 ± 0.063  ns/op
CleanerChurn.test      N/A         2048  avgt    9   4.671 ± 0.071  ns/op

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

PR Comment: https://git.openjdk.org/jdk/pull/22043#issuecomment-2470928360