RFR: 8317453: NMT: Performance benchmarks are needed to measure speed and memory

[David Holmes]

On Tue, 14 Jan 2025 19:12:45 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

> Here is another, hopefully, closer to the final iteration of NMT benchmarking mechanism.
> 
> To use, you first need to record the pattern of operations, ex:
> 
> `./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NMTRecordMemoryAllocations=0x7FFFFFFF -jar build/macosx-aarch64-server-release/images/jdk/demo/jfc/J2Ddemo/J2Ddemo.jar`
> 
> This will run the target app, and log all the allocations in chronological order. This will produce a few files:
> - hs_nmt_pid22770_allocs_record.log (is the chronological record of the the desired operations)
> - hs_nmt_pid22770_info_record.log (is the record of default NMT memory overhead and the NMT state)
> - hs_nmt_pid22770_threads_record.log (is the record of thread names that can be retrieved later when processing)
> 
> Now you can use those recording to actually benchmark your proposed changes, ex:
> 
> `./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NMTBenchmarkRecordedPID=22770 -XX:NMTBenchmarkRecordedLoops=10`
> 
> Which will produce yet another file:
> 
> - hs_nmt_pid23527_benchmark.log
> 
> that contains the details of the session, which can be further processed and analyzed by a tool, such as the one in jdk/src/utils/nmt, however, if you are looking just for one performance number look for `time:2744190[ns] [samples:115263]` in the output.
> 
> The total time for this particular run is 2,744,190 nanosecond or ~2.7 seconds, which you can use to compare `before` and `after` your change.

I'm really not sure what this is actually trying to benchmark - who will be collecting this data and analysing it and what will they do with their results?

That aside, generating the logs in a training run is okay, but the tool for processing those logs should reside elsewhere.

A few initial passing comments.

src/demo/share/jfc/J2Ddemo/java2d/Intro.java line 449:

> 447:                   System.exit(0);
> 448:               }
> 449:               Scene scene = director.get(index);

Leftover debugging code?

src/hotspot/share/nmt/memLogRecorder.cpp line 27:

> 25: // record pattern of allocations of memory calls:
> 26: //
> 27: // ./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NMTRecordMemoryAllocations=0x7FFFFFFF -jar build/macosx-aarch64-server-release/images/jdk/demo/jfc/J2Ddemo/J2Ddemo.jar

You don't need the full paths in these examples

src/hotspot/share/nmt/memLogRecorder.cpp line 43:

> 41: // then to actually run the benchmark:
> 42: //
> 43: // ./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NMTBenchmarkRecordedPID=43100 -XX:NMTBenchmarkRecordedLoops=10

?? How does this run anything - you haven't passed an initial class to the Java invocation?

src/hotspot/share/nmt/memLogRecorder.cpp line 98:

> 96:  // ???
> 97: #endif
> 98:   pthread_mutex_init(&_mutex, NULL);

You need to use existing synchronization API here. Either Mutex or PlatformMutex depending on initialization constraints; maybe a Semaphore if the others can't work.

src/hotspot/share/nmt/memLogRecorder.hpp line 37:

> 35: #elif defined(WINDOWS)
> 36:  // ???
> 37: #endif

You need to use existing synchronization API here. Either Mutex or PlatformMutex depending on initialization constraints; maybe a Semaphore if the others can't work.

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

Changes requested by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23115#pullrequestreview-2557544778
PR Review Comment: https://git.openjdk.org/jdk/pull/23115#discussion_r1919324156
PR Review Comment: https://git.openjdk.org/jdk/pull/23115#discussion_r1919325893
PR Review Comment: https://git.openjdk.org/jdk/pull/23115#discussion_r1919328324
PR Review Comment: https://git.openjdk.org/jdk/pull/23115#discussion_r1919328661
PR Review Comment: https://git.openjdk.org/jdk/pull/23115#discussion_r1919324004