[Llvm-bgq-discuss] Details behind MPI wrapper for bgclang++

[Michael Blocksome]

All,

I seem to be getting duplicates of each email in this thread .. any idea 
what's going on with the mailing list?

Michael Blocksome
Blue Gene Messaging
blocksom at us.ibm.com




From:   Jack Poulson <jack.poulson at gmail.com>
To:     Hal Finkel <hfinkel at anl.gov>, 
Cc:     llvm-bgq-discuss at lists.alcf.anl.gov
Date:   02/28/2013 09:44 PM
Subject:        Re: [Llvm-bgq-discuss] Details behind MPI wrapper for 
bgclang++
Sent by:        llvm-bgq-discuss-bounces at lists.alcf.anl.gov



On Thu, Feb 28, 2013 at 7:36 PM, Hal Finkel <hfinkel at anl.gov> wrote:
----- Original Message -----
> From: "Jack Poulson" <jack.poulson at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "Jeff Hammond" <jhammond at alcf.anl.gov>, 
llvm-bgq-discuss at lists.alcf.anl.gov
> Sent: Thursday, February 28, 2013 7:40:19 PM
> Subject: Re: [Llvm-bgq-discuss] Details behind MPI wrapper for bgclang++
>
> On Thu, Feb 28, 2013 at 5:24 PM, Hal Finkel < hfinkel at anl.gov >
> wrote:
>
>
>
>
> ----- Original Message -----
> > From: "Jack Poulson" < jack.poulson at gmail.com >
> > To: "Hal Finkel" < hfinkel at anl.gov >
> > Cc: "Jeff Hammond" < jhammond at alcf.anl.gov >,
> > llvm-bgq-discuss at lists.alcf.anl.gov
>
> > Sent: Thursday, February 28, 2013 6:51:08 PM
> > Subject: Re: [Llvm-bgq-discuss] Details behind MPI wrapper for
> > bgclang++
> >
>
> > Thanks Hal, that helps clear things up a bit. I guess I should be a
> > little more clear about what exactly I'm doing. Since CMake's
> > FindMPI module seems to attempt to link to MPICH incorrectly if I
> > directly specify the mpic++11, I have to instead manually specify
> > its behaviour (and thankfully Jeff took care of this a month or two
> > ago). One of my link commands generated by CMake looks like this:
> >
> >
> >
> > /home/projects/llvm/bin/bgclang++ -Wall -std=c++11 -O3
> > -stdlib=libc++
> > -L/bgsys/drivers/ppcfloor/comm/gcc/lib
> > -L/bgsys/drivers/ppcfloor/comm/sys/lib
> > -L/bgsys/drivers/ppcfloor/spi/lib
> > CMakeFiles/HypRadon-2d.dir/test/transform/HypRadon-2d.cpp.o -o
> > bin/transform/HypRadon-2d -rdynamic libcmake-dummy-lib.a
> > -L/soft/libraries/alcf/current/gcc/LAPACK/lib -llapack
> > -L/soft/libraries/essl/current/essl/5.1/lib64 -lesslbg
> > -L/soft/compilers/ibmcmp-nov2012/xlf/bg/14.1/bglib64 -lxlf90_r
> > -L/soft/compilers/ibmcmp-nov2012/xlsmp/bg/3.1/bglib64 -lxlomp_ser
> > -L/soft/compilers/ibmcmp-nov2012/xlmass/bg/7.3/bglib64 -lmassv
> > -lmass -lxlopt -lxlfmath -lxl -lgfortran -lm -lpthread -ldl
> > -Wl,--allow-multiple-definition -lcxxmpich -lmpich -lopa -lmpl -ldl
> > -lpami -lSPI -lSPI_cnk -lpthread -lrt -lstdc++
> >
> >
> > Upon typing this, I noticed that both libc++ and libstdc++ are both
> > being used (which I assume is bad).
>
> Actually, this is okay (although this is not obvious). When you
> specify -stdlib=libc++ the clang driver automatically rewrites
> -lstdc++ to some system-specific set of libraries necessary to link
> with libc++. In our case, this is -lc++ (and -lrt -lpthread -lstdc++
> when statically linking). As a result, using -lstdc++ is fine here.
> You can verify this by passing -v and examining the linking command
> line.
>
> I should also note that we have a *special* libc++ install which is
> partially based on libstdc++ so that we can link statically with
> PAMI without symbol definition conflicts. Everything *should* work,
> but I've only done some limited testing.
>
> So using the command-line above succeeds but produces an executable
> that crashes?
>
>
>
>
>
>
> Hi Hal,
>
>
> Thanks, that makes a lot of sense! The executable Backproj-2d in
> /home/poulson/dist-butterfly/build/clang/bin/transform produced
> core.{0,6,8,10,11}. Please let me know if you do not have access for
> some reason, and thank you again for your help.

Interesting; so the backtrace is messed up, but the problem seems 
legitimate. The code is ending up in steady_clock::now(), which uses 
clock_gettime(CLOCK_MONOTONIC, ...), which is not supported on the BG/Q 
compute nodes. I'll need to change it to use CLOCK_REALTIME instead; I'll 
let you know when to retry.

Thanks again,
Hal


Thanks Hal! I was thrown off by the fact that the trace contained 
MPI_Gather and the program had failed before it should have reached any 
MPI_Gather calls.  I very much appreciate the help.

Jack_______________________________________________
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