[Openmp-dev] Performance slowdown

[Bataev, Alexey via Openmp-dev]

Yes, but still this version is not optimal. Clang trunk will produce a 
little bit faster code.

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

19.08.2015 23:39, Finkel, Hal J. via Openmp-dev пишет:
> /
> /
> /Sent from my Verizon Wireless 4G LTE DROID/
> /On Aug 19, 2015 1:36 PM, César via Openmp-dev 
> <//openmp-dev at lists.llvm.org/ <mailto:openmp-dev at lists.llvm.org>/> wrote:/
> />/
> /> On Wed, Aug 19, 2015 at 3:07 PM, Jack Howarth 
> <//howarth.mailing.lists at gmail.com/ 
> <mailto:howarth.mailing.lists at gmail.com>/> wrote:/
> />>/
> />> On Tue, Aug 18, 2015 at 2:14 PM, César via Openmp-dev/
> />> <//openmp-dev at lists.llvm.org/ <mailto:openmp-dev at lists.llvm.org>/> 
> wrote:/
> />> > 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>
> />>/
> />> That web page claims the benchmarks use parts of the OpenMP 4.0 
> specification./
> />>/
> />> "The KaStORS benchmark suite has been designed to evaluate the 
> implementation of/
> />> the OpenMP dependent task paradigm, introduced as part of the 
> OpenMP 4.0/
> />> specification."/
> />>/
> />> Currently openmp is only complete for the OpenMP 3.2 specification/
> />>/
> />/
> /> I am able to compile a few benchmarks that use task dependence 
> annotations (from OMP 4.0) but for those that specify the range of the 
> memory dependence I get syntax error. So, should I assume that this 
> part is not implemented, right? Is there a list for the OMP 4.0 items 
> that are currently supported?/
> />/
> /> BTW, the Clang version from Github was able to parse these 
> annotations, was it dropped from the current newer version?/
> />/
> /
> /
> /It is not there yet. You'll need to use the code from the github 
> clang_trunk (and llvm_trunk, etc.) repositories to get both recent 
> Clang/LLVM and all of the OpenMP features./
> /
> /
> /-Hal/
> /
> /
> /> /
> />>/
> />> >/
> />> > 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./
> />> >/
> />> > _______________________________________________/
> />> > 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/
> />> >/
> />/
> />/
> /
> /
>
> /Sent from my Verizon Wireless 4G LTE DROID/
>
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