[Openmp-dev] Performance slowdown

[Bataev, Alexey via Openmp-dev]

If you're using 3.5, then this is unofficial version with OpenMP. Use 
3.7 instead just like Andrey said

Best regards,
Alexey Bataev
=============
Software Engineer
Intel Compiler Team

19.08.2015 1:25, César via Openmp-dev пишет:
> Hi Andrey,
>
> this is strange because when I compile with "clang-3.5 -fopenmp" the 
> executable that is produced is parallel. I am sure of this because I'm 
> able to see the threads and also because I can see the symbols used by 
> the IOMP runtime in the binary.
>
> $ clang -O3 -g -fopenmp toy13.cpp -o toy13 -lm
>
> $ nm toy13 | grep kmpc
> U __kmpc_cancel_barrier@@VERSION
> U __kmpc_end_single@@VERSION
> U __kmpc_fork_call@@VERSION
> U __kmpc_omp_task_alloc@@VERSION
> U __kmpc_omp_task_with_deps@@VERSION
> U __kmpc_single@@VERSION
>
> $ ldd toy13
> linux-vdso.so.1 =>  (0x00007fff9805d000)
> libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fc00e3cc000)
> libiomp5.so => /usr/lib/libiomp5.so (0x00007fc00e121000)
> libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 
> (0x00007fc00df03000)
> libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fc00db3e000)
> libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fc00d939000)
> /lib64/ld-linux-x86-64.so.2 (0x00007fc00e6fc000)
>
>
>
>
>
> César.
>
> On Tue, Aug 18, 2015 at 6:15 PM, <andreybokhanko at gmail.com 
> <mailto:andreybokhanko at gmail.com>> wrote:
>
>     César,
>
>>     - The version of Clang that I am using to compile the benchmarks:
>>     3.5.0
>
>     Clang 3.5 doesn't support OpenMP -- it simply ignores the pragmas.
>
>     Please use version from trunk or from 3_7 release branch. Also,
>     please supply -fopenmp= libomp option.
>
>     Yours,
>     Andrey Bokhanko
>     =============
>     Software Engineer
>     Intel Compiler Team
>     Intel
>
>     Отправлено с iPad
>
>     18 авг. 2015 г., в 21:14, César via Openmp-dev
>     <openmp-dev at lists.llvm.org <mailto:openmp-dev at lists.llvm.org>>
>     написал(а):
>
>>     Hello,
>>
>>     I don't know if this is the correct list to talk about this - I
>>     did not find a better place..
>>
>>     I am doing performance experiments with a few OpenMP
>>     implementations (IOMP, GOMP and our private impl.) and I am
>>     seeing a severe slowdown when I use IOMP (GOMP and others are
>>     performing well).
>>
>>     The benchmarks I am using are these ones:
>>     http://kastors.gforge.inria.fr/#!index.md
>>     <http://kastors.gforge.inria.fr/#%21index.md>
>>
>>     Really, the slowdown is huge. For one of the programs
>>     (plasma/dpotrf_taskdep -n 8192 -b 64 -i 1 -c) the serial version
>>     executes in ~28s and the parallel one executes in ~110s. I did
>>     some profiling and found that most of the time is being spent on
>>     synchronization barriers and dependence tracking (see attached
>>     image). Before digging deeper I would like to hear back from you
>>     if I am doing something wrong here:
>>
>>     - I tested with the last version of the repository:
>>     http://llvm.org/svn/llvm-project/openmp/trunk
>>     - I am using Ubuntu 14.10.
>>     - I have tested on more than one machine, the results above are
>>     from a Intel i7-3770
>>     - The runtime itself is compiled using: make compiler=gcc
>>     os_omp=linux arch=32e
>>     - The version of GCC that I am using is: 4.9.1
>>     - The version of Clang that I am using to compile the benchmarks:
>>     3.5.0
>>
>>
>>     César.
>>     <pic1.png>
>>     <pic2.png>
>>     <pic3.png>
>>     _______________________________________________
>>     Openmp-dev mailing list
>>     Openmp-dev at lists.llvm.org <mailto:Openmp-dev at lists.llvm.org>
>>     http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>
>
>
>
> _______________________________________________
> Openmp-dev mailing list
> Openmp-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/openmp-dev/attachments/20150819/85153638/attachment-0001.html>