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Subject: Re: [OMPI devel] Old Linux kernels
From: Paul H. Hargrove (PHHargrove_at_[hidden])
Date: 2011-03-15 18:46:46


Sorry, I stated my facts backwards.
CORRECTED facts:

+The old "LinuxThreads" implementation is the one that gave DIFFERENT
pids to each pthread.
+ "NPTL" is the current implementation of Pthreads for Linux, and the
one giving a single pid shared by all pthreads.

So, I hope Ralph's statement is similarly reversed, because
"LinuxThreads" as not been maintained in years.

-Paul

On 3/15/2011 3:40 PM, Ralph Castain wrote:
> I believe the test is intended strictly for Linux threads. I don't believe we have ever (intentionally) supported any other thread library in such environments.
>
> I'll leave it to Jeff to decide if he feels this is an issue.
>
>
> On Mar 15, 2011, at 4:27 PM, Paul H. Hargrove wrote:
>
>> I'd like to point out that it is libpthread and the arguments it passes to clone(), NOT the Linux kernel version, that is the determining factor (at least if you have a 2.6.x kernel). The "LinuxThreads" implementation of Pthreads will give the one-pid-to-rule-them all behavior, while the NPTL implementation gives unquie pids under any 2.6.x kernel and even w/ some 2.4.x kernels from Red Hat.
>>
>> I have encountered systems on which dynamic linking gave NPTL and static linking gave LinuxThreads. That is a "gottcha" that I am not certain Jeff and Ralph have taken into account.
>>
>> Note that I have no objection to "we don't support this", but fear that detection of that situation may be flawed.
>>
>> -Paul
>>
>> On 3/15/2011 2:14 PM, Ralph Castain wrote:
>>> Hi folks
>>>
>>> Jeff and I encountered a problem when cross-compiling OMPI for Linux. Turned out that we had an old test in the code that looked for threads to have different pids. Since it couldn't be tested when cross-compiling, the test simply assumed this was the case for Linux under those conditions - which broke the build for current Linux kernels.
>>>
>>> Different pids for threads was last seen in the old RH 4 series (kernel 2.6.9 or so). Some code (e.g., waitpid) was also provided to support this unusual situation - this code was in fact broken when we updated the event library. So even if we were in an old kernel, the code base would neither compile nor run.
>>>
>>> Rather than trying to continue to support these old kernels, we have removed all the stale code that was covered by OPAL_THREADS_HAVE_DIFFERENT_PIDS. This removed some complexity from a few PLM modules and removed the broken code.
>>>
>>> Jeff modified the corresponding .m4 test so we now detect an older kernel, print out a nice "we don't support this" message (along with noting that earlier versions of OMPI do), and then abort the build.
>>>
>>> If you know of some reason to restore support for old Linux kernels, and someone willing to do the work to "refresh" that support, please let us know.
>>>
>>> Ralph& Jeff
>>>
>>>
>>> _______________________________________________
>>> devel mailing list
>>> devel_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>> --
>> Paul H. Hargrove PHHargrove_at_[hidden]
>> Future Technologies Group
>> HPC Research Department Tel: +1-510-495-2352
>> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
>>
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>
> _______________________________________________
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-- 
Paul H. Hargrove                          PHHargrove_at_[hidden]
Future Technologies Group
HPC Research Department                   Tel: +1-510-495-2352
Lawrence Berkeley National Laboratory     Fax: +1-510-486-6900