[Openmp-dev] Performance slowdown

[andreybokhanko via Openmp-dev]

Indeed, I meant official released 3.5. Did you get your compiler from clang-omp.github? It's probably outdated and can't be used for reliable performance measurements.

I will update clang-omp.github home page to avoid further confusion.

Yours,
Andrey

> 19 авг. 2015 г., в 8:17, Bataev, Alexey <a.bataev at hotmail.com> написал(а):
> 
> 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> 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> 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
>>>> 
>>>> 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
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>> 
>> 
>> 
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> 
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