[Openmp-dev] Performance slowdown

[César via Openmp-dev]

Hello,

On Aug 20, 2015 5:44 AM, "Churbanov, Andrey" <Andrey.Churbanov at intel.com>
wrote:
>
> Actually the performance problem is separate from
>
> supported version or linker errors or compiler used.
>
>

That was my first thought.

>
> So we apparently need to investigate the problem
>
> in the OpenMP runtime. We will work on this.
>

I will also spend some time investigating the problem in the runtime.

Thank you,

>
> Thanks,
>
> Andrey
>
>
>
> From: Openmp-dev [mailto:openmp-dev-bounces at lists.llvm.org] On Behalf Of
Bataev, Alexey via Openmp-dev
> Sent: Thursday, August 20, 2015 6:08 AM
> To: Finkel, Hal J.
>
> Cc: openmp-dev at lists.llvm.org
> Subject: Re: [Openmp-dev] Performance slowdown
>
>
>
> 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>
wrote:
>>
>> >
>>
>> > On Wed, Aug 19, 2015 at 3:07 PM, Jack Howarth <
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> 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
>>
>> >>
>>
>> >> 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
>>
>> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>>
>> >> >
>>
>> >
>>
>> >
>>
>>
>>
>>
>>
>> Sent from my Verizon Wireless 4G LTE DROID
>>
>>
>>
>>
>> _______________________________________________
>>
>> Openmp-dev mailing list
>>
>> Openmp-dev at lists.llvm.org
>>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>
>
>
>
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