Re: [boost] [random] new threefry random engine

Subject: Re: [boost] [random] new threefry random engine
From: Thijs van den Berg (thijs_at_[hidden])
Date: 2014-05-07 05:36:26

I did some performance test, with 4 threads -O3 and ITERATIONS = 10.000.000, and there is no performance difference between the two versions (see below). My opinion is that we should stick with a standard random engine concept I used, merge our code (we both have non-overlapping bits that are needed), and think a bit more about random function concepts at a later stage. For me a random engine is al I need.

timings:    7534.86    7603.93 ms
timings:    7640.01    7533.52 ms
timings:     7648.3    7604.28 ms
timings:    7595.59    7626.43 ms
timings:    6767.75    6432.64 ms
timings:    7635.71     7535.7 ms
timings:    7604.28    7618.24 ms
timings:    7734.14    7091.38 ms
timings:    7366.14    7581.43 ms
timings:    7559.15    7168.32 ms
timings:    7538.35    7355.96 ms
timings:    7476.68    7702.23 ms
timings:    6757.96    7545.04 ms
timings:     7607.6     7608.7 ms
timings:    7608.16    7657.03 ms
timings:    6886.66     7698.5 ms
timings:    6833.46    6466.57 ms
timings:    7624.62     6443.1 ms
timings:    6741.91    6464.72 ms
timings:    7464.41    6428.27 ms

left:

void thermalize(atom* atoms, size_t Natoms, uint32_t timestep, const Prf::key_type& key){
    counter_based_engine<Prf, 32> cbeng(key);
    for(size_t i=0; i<Natoms; ++i){
        float rmsvelocity = sqrt(kT/atoms[i].mass);
        normal_distribution<float> mbd(0., rmsvelocity);
        Prf::domain_type start = {atoms[i].id, timestep, THERMALIZE_CTXT};
        cbeng.restart(start);
        for (size_t j=0; j<ITERATIONS; ++j) {
            atoms[i].vx += mbd(cbeng);
            atoms[i].vy += mbd(cbeng);
            atoms[i].vz += mbd(cbeng);
        }
    }
}

right:

void thermalize_std(atom* atoms, size_t Natoms, uint32_t timestep){
    for(size_t i=0; i<Natoms; ++i){ 
        float rmsvelocity = sqrt(kT/atoms[i].mass);
        normal_distribution<float> mbd(0., rmsvelocity);
        threefry4x64_engine<uint32_t, 32, 20, 1, 1> eng(i);
        for (size_t j=0; j<ITERATIONS; ++j) {
            atoms[i].vx += mbd(eng);
            atoms[i].vy += mbd(eng);
            atoms[i].vz += mbd(eng);
        }
    }
}