Performance improvement in PureJavaCrc32
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Key: HADOOP-7333
URL: https://issues.apache.org/jira/browse/HADOOP-7333
Project: Hadoop Common
Issue Type: Improvement
Components: util
Affects Versions: 0.21.0
Environment: Linux x64
Reporter: Eric Caspole
Priority: Minor
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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