RFR: 8284849: Add deoptimization to unified logging [v3]

[John R Rose]

On Wed, 1 Jun 2022 11:59:36 GMT, Johan Sjölén <duke at openjdk.java.net> wrote:

>> This PR adds a new "deoptimization" tag and a new log message on the info level mimicking JFR's deoptimization event. In the future this tag will be used to add trace level information, hopefully replacing TraceDeoptimization. JFR's event also captures the stacktrace, which this does not (happy to add this if considered important).
>> 
>> An example output looks like this: 
>> 
>> 
>> [1.346s][info][deoptimization] Deoptimization start {
>> [1.346s][info][deoptimization]   compileId = 407
>> [1.346s][info][deoptimization]   compiler = c2
>> [1.346s][info][deoptimization]   method:lineno:bci = java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(I)Z:176:26
>> [1.346s][info][deoptimization]   instruction = ifne
>> [1.346s][info][deoptimization]   reason = unstable_if
>> [1.346s][info][deoptimization]   action = reinterpret
>> [1.346s][info][deoptimization] } Deoptimization end
>
> Johan Sjölén has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove superfluous if stmt

>  In the future this tag will be used to add trace level information, hopefully replacing TraceDeoptimization.

That trace-level information has a variable number of backtrace records in it:

https://github.com/openjdk/jdk/blob/6030c0e4033655e7ce282f43c2216b4e29411c22/src/hotspot/share/runtime/deoptimization.cpp#L1567

UL support for TraceDeoptimization will need to ensure that these complex aggregate events, consisting of multiple UL lines, are kept together.  Normal JVM concurrency will (otherwise) occasionally damage the TraceDeoptimization by interleaving individual UL lines that belong to separate complex aggregate events.

I note that you started with a multi-line format at the top of this PR, and went somewhere else.  Good move, but it only works until we need to output a variable amount of supporting event detail.

The integration of https://github.com/openjdk/jdk/pull/8748 is a *big* step in that direction.

FTR here are some notes from me about how existing complex output from HotSpot stresses the boundaries of UL:

https://bugs.openjdk.java.net/browse/JDK-8046148?focusedCommentId=13568278&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-13568278

Good work.

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PR: https://git.openjdk.java.net/jdk/pull/8812