Oral Presentation

Acceleration of the tree method with SIMD instruction set

Author(s): Tetsushi Kodama (Chiba University); Tomoaki Ishiyama (Chiba University)

Presenter: Tetsushi Kodama (Chiba University)

We have developed a highly-tuned software library that accelerates the
calculation of quadrupole terms in the Barnes-Hut tree code by use of
a SIMD instruction set on the x86 architecture, Advanced Vector
eXtensions 2 (AVX2). Our code is implemented as an extension of
Phantom-GRAPE software library that significantly accelerates the
calculation of monopole terms. If the same accuracy is required, the
calculation of quadrupole terms can accelerate the evaluation of forces
than that of only monopole terms because we can approximate
gravitational forces from closer particles by quadrupole moments than
by only monopole moments. Our implementation can calculate
gravitational forces about 1.1 times faster in any system than the
combination of the pseudoparticle multipole method and Phantom-GRAPE.
Our implementation allows simulating homogeneous systems up to 2.2
times faster than that with only monopole terms, however, speed up for
clustered systems is not enough because the increase of approximated
interactions is insufficient to negate the increased calculation cost
by computing quadrupole terms. We have estimated that improvement in
performance can be achieved by the use of a new SIMD instruction set,
AVX-512. Our code is expected to be able to accelerate simulations of
clustered systems up to 1.08 times faster on AVX-512 environment than
that with only monopole terms.