Thread-level parallelization and optimization of NWChem for the Intel MIC architecture

Conference · Thu Jan 01 04:00:00 EST 2015

DOI:https://doi.org/10.1145/2712386.2712391· OSTI ID:1407275

Shan, Hongzhang ^[1]; Williams, Samuel ^[1]; de Jong, Wibe ^[1]; Oliker, Leonid ^[1]

---

1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

In the multicore era it was possible to exploit the increase in on-chip parallelism by simply running multiple MPI processes per chip. Unfortunately, manycore processors' greatly increased thread- and data-level parallelism coupled with a reduced memory capacity demand an altogether different approach. In this paper we explore augmenting two NWChem modules, triples correction of the CCSD(T) and Fock matrix construction, with OpenMP in order that they might run efficiently on future manycore architectures. As the next NERSC machine will be a self-hosted Intel MIC (Xeon Phi) based supercomputer, we leverage an existing MIC testbed at NERSC to evaluate our experiments. In order to proxy the fact that future MIC machines will not have a host processor, we run all of our experiments in native mode. We found that while straightforward application of OpenMP to the deep loop nests associated with the tensor contractions of CCSD(T) was sufficient in attaining high performance, significant e ort was required to safely and efeciently thread the TEXAS integral package when constructing the Fock matrix. Ultimately, our new MPI+OpenMP hybrid implementations attain up to 65× better performance for the triples part of the CCSD(T) due in large part to the fact that the limited on-card memory limits the existing MPI implementation to a single process per card. Additionally, we obtain up to 1.6× better performance on Fock matrix constructions when compared with the best MPI implementations running multiple processes per card.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC-21)
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 1407275
• Country of Publication: United States
• Language: English

Related Subjects

CCSD(T)
Fock Matrix Construction
MPI
Manycore Architecture
NWChem
OpenMP
OpenMP Task
Performance
Texas Integral
Thread-level Parallelism