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Posted to mapreduce-issues@hadoop.apache.org by "Alan Burlison (JIRA)" <ji...@apache.org> on 2015/07/22 21:11:06 UTC
[jira] [Updated] (MAPREDUCE-6391) util/Timer.cc completely
misunderstands _POSIX_CPUTIME
[ https://issues.apache.org/jira/browse/MAPREDUCE-6391?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Alan Burlison updated MAPREDUCE-6391:
-------------------------------------
Attachment: MAPREDUCE-6391
> util/Timer.cc completely misunderstands _POSIX_CPUTIME
> ------------------------------------------------------
>
> Key: MAPREDUCE-6391
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6391
> Project: Hadoop Map/Reduce
> Issue Type: Sub-task
> Components: build
> Affects Versions: 2.7.0
> Reporter: Alan Burlison
> Assignee: Alan Burlison
> Attachments: MAPREDUCE-6391
>
>
> util/Timer.cc contains the following code:
> clock_gettime(_POSIX_CPUTIME, &ts);
> I'm not exactly sure what sort of time value this code is attempting to obtain (the process's on-CPU time perhaps?) but it is completely wrong, even on Linux. _POSIX_CPUTIME is a feature test macro and is *not* a valid parameter to clock_gettime. From the clock_gettime manpage:
> bq. The symbols _POSIX_MONOTONIC_CLOCK, _POSIX_CPUTIME, _POSIX_THREAD_CPUTIME indicate that CLOCK_MONOTONIC, CLOCK_PROCESS_CPUTIME_ID, CLOCK_THREAD_CPUTIME_ID are available
> On my Linux distro the value of _POSIX_CPUTIME is defined as 0. That corresponds to
> bq. #define __CLOCK_REALTIME0 0 /* obsolete; same as CLOCK_REALTIME */
> And CLOCK_REALTIME is
> bq. #define CLOCK_REALTIME 3 /* wall clock */
> Which I suspect is not what is required here.
> Getting cross-platform CPU time is fiddly, the following blog post has a good summary: http://nadeausoftware.com/articles/2012/03/c_c_tip_how_measure_cpu_time_benchmarking (code examples are CC licensed so should be no taint issues)
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