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https://issues.apache.org/jira/browse/LOG4J2-2478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16650092#comment-16650092
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ASF GitHub Bot commented on LOG4J2-2478:
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GitHub user DiegoEliasCosta opened a pull request:
https://github.com/apache/logging-log4j2/pull/219
LOG4J2-2478 Return the computed variables on each benchmark to avoid DCE
As mentioned in [JIRA](https://issues.apache.org/jira/browse/LOG4J2-2478),
this patch simply returns the computation on every benchmark that uses the
static _consume_ method. We do that to prevent dead-code elimination, which is
only partially addressed in the current implementation.
Another patch that could simplify the benchmark code, and get considerably
faster throughputs, would be to simply rely on _Blackhole.consume_ methods to
sink the computation. We then, would not need the _consume_ method we have in
the class.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/DiegoEliasCosta/logging-log4j2
jmh-antipatterns-ignoredreturn
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/logging-log4j2/pull/219.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #219
----
commit 59a41bb5dbe2f5edba9c4b7eb68f309ad7f637ce
Author: DiegoEliasCosta <diegoelias1@...>
Date: 2018-10-15T11:21:30Z
LOG4J2-2478 Return the computed variables on each benchmark to avoid DCE
----
> JMH Benchmarks in not consuming all computed variables (risk of DCE)
> --------------------------------------------------------------------
>
> Key: LOG4J2-2478
> URL: https://issues.apache.org/jira/browse/LOG4J2-2478
> Project: Log4j 2
> Issue Type: Bug
> Components: Tests
> Environment: I am reporting the result of 5 full executions with
> default parameters (iterations, forks, warmups, etc..)
> Tests run on a Computational server with CPU: E5-1660-3.3GHZ (6 cores + HT),
> 64 GB RAM.
> Reporter: Diego Elias Damasceno Costa
> Priority: Minor
> Attachments: logginglog4j2-jmhantipatterns-retu.csv
>
>
> We are conducting a scientific study to investigate bad
> practices/anti-patterns on creating micro-benchmarks using JMH, and we found
> an instance of harmfull non-consumed computation in
> `AbstractStringLayoutStringEncodingBenchmark`.
> As a good practice, every computation performed in inside the benchmark
> should be consumed (see [JMH
> Documentation|[http://hg.openjdk.java.net/code-tools/jmh/file/66fb723292d4/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java].]
>
> This is partially done here with the self-made consume method, but on some
> benchmarks (such as baseline, usAsciiGetBytes) the return is not consumed in
> the benchmark, which opens the possibility of a Dead-Code Elimination to be
> performed by JVM.
> *There is a very simple solution:* just return the long primitive calculated
> by _consume()_ at the end of each benchmark. This is done on other benchmarks
> of the project as well.
> In our tests, benchmarks were lightly affected (see attachment), with
> Throughputs 5-35% lower after our fix patch.
>
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