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https://issues.apache.org/jira/browse/HADOOP-8926?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gopal V updated HADOOP-8926:
----------------------------
Status: Open (was: Patch Available)
Reworking for readability of code
> hadoop.util.PureJavaCrc32 cache hit-ratio is low for static data
> ----------------------------------------------------------------
>
> Key: HADOOP-8926
> URL: https://issues.apache.org/jira/browse/HADOOP-8926
> Project: Hadoop Common
> Issue Type: Improvement
> Components: util
> Affects Versions: 2.0.3-alpha
> Environment: Ubuntu 10.10 i386
> Reporter: Gopal V
> Assignee: Gopal V
> Priority: Trivial
> Labels: optimization
> Attachments: crc32-faster+test.patch, pure-crc32-cache-hit.patch
>
>
> While running microbenchmarks for HDFS write codepath, a significant part of
> the CPU fraction was consumed by the DataChecksum.update().
> The attached patch converts the static arrays in CRC32 into a single linear
> array for a performance boost in the inner loop.
> milli-seconds for 1Gig (16400 loop over a 64kb chunk)
> || platform || original || cache-aware || improvement ||
> | x86 | 3894 | 2304 | 40.83 |
> | x86_64 | 2131 | 1826 | 14 |
> The performance improvement on x86 is rather larger than the 64bit case, due
> to the extra register/stack pressure caused by the static arrays.
> A closer analysis of the PureJavaCrc32 JIT code shows the following assembly
> fragment
> {code}
> 0x40f1e345: mov $0x184,%ecx
> 0x40f1e34a: mov 0x4415b560(%ecx),%ecx ;*getstatic T8_5
> ; - PureJavaCrc32::update@95 (line 61)
> ; {oop('PureJavaCrc32')}
> 0x40f1e350: mov %ecx,0x2c(%esp)
> {code}
> Basically, the static variables T8_0 through to T8_7 are being spilled to the
> stack because of register pressure. The x86_64 case has a lower likelihood of
> such pessimistic JIT code due to the increased number of registers.
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