Re: [Boost-mpi] Suboptimal sending of std::vectors

Subject: Re: [Boost-mpi] Suboptimal sending of std::vectors
From: Simon Etter (ettersi_at_[hidden])
Date: 2014-01-20 10:17:24

Only in the plain array benchmark I don't measure memory allocation. For both the skeleton and plain array sending of a std::vector, the memory 
allocation (and zero initialization) is included in the benchmark. Since I am interested in the performance of sending an amount of data not 
previously known by the receiver, I would rather include the memory allocation also for the plain array benchmark. However, the plain array 
benchmark is only there to give an upper bound. To make my point, comparing the three benchmarks involving std::vectors is sufficient, and these 
three benchmarks should be equivalent in terms of the work that is done.

On 20/01/14 15:37, Gonzalo Brito Gadeschi wrote:
> You should call vector.reserve(n) before you call recv and benchmark again because otherwise you are timing a memory allocation in the vector
> benchmarks that isn't there in the array benchmarks.
>
> Bests,
> Gonzalo
>
>
>
> On Mon, Jan 20, 2014 at 3:24 PM, Simon Etter <ettersi_at_[hidden] <mailto:ettersi_at_[hidden]>> wrote:
>
>     Hi!
>
>     When benchmarking the performance of sending a std::vector<double> with Boost.MPI, I noticed that you can gain several factors of speedup if
>     you replace
>
>     std::vector<double> data(n);
>     comm.send(0,0,data);
>
>     by e.g.
>
>     std::vector<double> data(n);
>     comm.send(0,0, boost::mpi::skeleton(data));
>     comm.send(0,0, boost::mpi::get_content(data))__;
>
>     The code to benchmark, the measured data as well as a plot thereof are attached. Further parameters were:
>
>     MPI implementation: Open MPI 1.6.5
>     C++ compiler: gcc 4.8.2
>     Compiler flags: -O3 -std=c++11
>     mpirun parameter: --bind-to-core
>     CPU model: AMD Opteron(tm) Processor 6174
>
>     Why is it/what am I doing wrong that the default sending of std::vector<double> performs so badly?
>
>     Best regards,
>     Simon Etter
>
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>
>
>
> --
> Dipl.-Ing. Gonzalo Brito Gadeschi
> Institute of Aerodynamics and Chair of Fluid Mechanics
> RWTH Aachen University
> Wuellnerstraße 5a
> D-52062 Aachen
> Germany
> Phone: ++49-(0)241-80-94821
> Fax: ++49-(0)241-80-92257
> E-mail: g.brito_at_[hidden] <mailto:g.brito_at_[hidden]>
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>
>
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