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https://issues.apache.org/jira/browse/HADOOP-7333?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Suresh Srinivas updated HADOOP-7333:
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Component/s: performance
> Performance improvement in PureJavaCrc32
> ----------------------------------------
>
> Key: HADOOP-7333
> URL: https://issues.apache.org/jira/browse/HADOOP-7333
> Project: Hadoop Common
> Issue Type: Improvement
> Components: performance, util
> Affects Versions: 0.21.0
> Environment: Linux x64
> Reporter: Eric Caspole
> Assignee: Eric Caspole
> Priority: Minor
> Fix For: 0.23.0
>
> Attachments: HADOOP-7333.patch, c7333_20110526.patch
>
>
> I would like to propose a small patch to
> org.apache.hadoop.util.PureJavaCrc32.update(byte[] b, int off, int len)
> Currently the method stores the intermediate result back into the data member
> "crc." I noticed this method gets
> inlined into DataChecksum.update() and that method appears as one of the
> hotter methods in a simple hprof profile collected while running terasort and
> gridmix.
> If the code is modified to save the temporary result into a local and just
> once store the final result back into the data member, it results in slightly
> more efficient hotspot codegen.
> I tested this change using the the
> "org.apache.hadoop.util.TestPureJavaCrc32$PerformanceTest" which is embedded
> in the existing unit test for this class, TestPureJavaCrc32 on a variety of
> linux x64 AMD and Intel multi-socket and multi-core systems I have available
> to test.
> The patch removes several stores of the intermediate result to memory
> yielding a 0%-10% speedup in the
> "org.apache.hadoop.util.TestPureJavaCrc32$PerformanceTest" which is embedded
> in the existing unit test for this class, TestPureJavaCrc32.
>
> If you use a debug hotspot JVM with -XX:+PrintOptoAssembly, you can see the
> intermediate stores such as:
> 414 movq R9, [rsp + #24] # spill
> 419 movl [R9 + #12 (8-bit)], RDX # int ! Field PureJavaCrc32.crc
> 41d xorl R10, RDX # int
> The patch results in just one final store of the fully computed value.
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