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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (HADOOP-7401) Unit test TestPureJavaCRC32 warmup code warms up the not-so-important loop in PureJavaCRC32.update()
Date Fri, 17 Jun 2011 21:43:47 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-7401?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Tsz Wo (Nicholas), SZE reassigned HADOOP-7401:
----------------------------------------------

    Assignee: monica beckwith

Hi Monica, this is an interesting discovery!  Could you also post the results before and after
the patch?

BTW, you need to generate patches at the project root directory.  Otherwise, Hadoop QA could
not apply it.

> Unit test TestPureJavaCRC32 warmup code warms up the not-so-important loop in PureJavaCRC32.update()
> ----------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-7401
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7401
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: test
>    Affects Versions: 0.21.0
>         Environment: Solaris-Sparcv9; Solaris-AMD64
>            Reporter: monica beckwith
>            Assignee: monica beckwith
>            Priority: Minor
>             Fix For: 0.21.0
>
>         Attachments: HADOOP-7401.patch
>
>   Original Estimate: 1m
>  Remaining Estimate: 1m
>
> When the warmup code sequence in TestPureJavaCRC32.java is executed, it sends size=len=2
and due to the value of 'trials' in for loop in doBench(), the crc.update() gets run >
the compile threshold, thus providing the information that 'while 0<len<7' is a hot
loop and 'while len>7' is a cold loop. This brings the MB/s number for len > 7 in PureJavaCRC32.update()
way down (e.g. ~28.5% for size=len=65536).
> The workaround would be to use size=len=>7 (so just having size=len=2101 ahead of
size=len=2 will do the trick) in the warmup section. 

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