Open MPI logo

Open MPI Development Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Development mailing list

Subject: Re: [OMPI devel] Old Linux kernels
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2011-03-16 06:30:07


Is there a version in a pthreads header file that can be checked?

You're right that I am currently checking Linux kernel version, not pthread version. Note that this is *only* in cross-compiling environments; in non cross compiling situations, we actually test the behavior to see if threads have different PIDs or not.

Sent from my phone. No type good.

On Mar 15, 2011, at 7:41 PM, "Ralph Castain" <rhc_at_[hidden]> wrote:

> My point was just that we support the current implementation of pthreads - not any old one.
>
> Also, to clarify: Jeff actually tests to see what the thread library does. We only use the Linux kernel version when cross-compiling since we cannot, in that case, actually test the support. We know that old Linux kernels have the old implementation, so we exclude them. Anything else is hit-miss when cross-compiling.
>
>
> On Mar 15, 2011, at 4:46 PM, Paul H. Hargrove wrote:
>
>> 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
>>>
>>> _______________________________________________
>>> 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
>
>
> _______________________________________________
> devel mailing list
> devel_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/devel