Computer Architecture Simulation & Visualisation
The QCD Computer Simulation Project
The aims of the QCD Computer Simulation project were:
Parameterised hardware-software co-simulation models of the QCDOC
architecture were created using HASE and
experiments were conducted to investigate its performance. At the
same time, the capabilities of HASE were extended in response to the
demands placed on it by the requirements of these models.
- to build HASE simulation models of the QCDOC computer system
- to investigate the factors which influence the performance of QCD
- to explore the design parameter space of the models to investigate
variations in performance against a range of architectural parameters
in order to inform the design of subsequent generations of such computers
An extension to the project has been to introduce a metamodelling
scheme which allows for efficient generation of simulation models with
alternate system configurations. This has allowed us to model and
evaluate the IBM Bluegene/L architecture.
The QCD Computer Simulation project was supported by EPSRC (Grant
GR/R/27129) from May 2001 to April 2004. Further details can be found
in the EPSRC Final Report.
- Sadaf Alam
- Marcelo Cintra
- Roland Ibbett
- Anthony Kennedy
- Richard Kenway
- Frederic Mallet
Quantum Chromodynamics (QCD) describes
theoretically the strong interactions between quarks and gluons. One
of the essential features of QCD is that these elementary particles
are always bound together, confined inside mesons and baryons,
collectively called hadrons. This provides a challenge in relating
theoretical and practical results, since the Standard Model of
particle physics describes the interactions of the quarks and gluons,
not of the experimentally observed hadrons.
To relate the experimental observations to the predictions from the
Standard Model thus needs detailed evaluation of the hadronic
structure, relating the quark constituents to the observed hadronic
properties in a precise way. The only theoretical method to achieve
this, with full control of all sources of error, is via large-scale
numerical simulation: lattice QCD.
The UK QCD Collaboration
The UKQCD collaboration is one of the leading lattice QCD projects in
the world, having pioneered many successful applications to particle
physics phenomenology. It has recently been awarded JIF funding to
build the fastest computer in the world for simulating strong
The UKQCD machine will be based on the Columbia QCDOC
architecture. QCDOC is a natural evolution of the massively parallel
QCDSP machine which won the 1998 IEEE Gordon Bell prize for the best
price/performance high-end computer. The individual processing nodes
in QCDOC will be Power PC-based and interconnected in a 4-dimension
mesh with the topology of a torus. Each node in QDOC will be a single
applications specific integrated circuit (ASIC) containing a 500 MHz
440 PowerPC processor core with a 1 Gflops, 64-bit floating point unit
and 4 MBytes of on-chip memory together with a Direct Memory Access
(DMA) unit for moving data between on-chip and external memory. It
will also contains circuitry to support internode communication and an
Ethernet controller for a boot-diagnostic-I/O network.
Each processor will be capable of sending and receiving data from each
of its eight nearest neighbors in four dimensions at a rate of 500
Mbit/sec. This will provide a total off-node bandwidth of 8 Gbit/sec.
Each of these 16 communication channels will have its own DMA
capability allowing autonomous reads/writes from either on-chip or
external memory. As in the QCDSP machines, an efficient and
low-latency global sum, global max and broadcast capability will be
incorporated into the serial communication.
D. Chen, P. Chen, N. Christ, R. Edwards, G. Fleming, A. Gara,
S. Hansen, C. Jung, A. Kaehler, A. Kennedy, G. Kilcup, Y. Luo,
C. Malureanu, R. Mawhinney, J. Parsons, J. Sexton, C.Z. Sui, & P.
Vranas. "QCDSP: A teraflop scale massively parallel supercomputer"
Technical Report, SCRI, 1997, ACM/IEEE SC97, 1997.
D. Chen, P. Chen, N. H. Christ, R. G. Edwards, G. Fleming, A. Gara,
S. Hansen, C. Jung, A. Kahler, S. Kasow, A.D. Kennedy, G. Kilcup,
Y. Luo, C. Malureanu, R.D. Mawhinney, J. Parsons, C. Sui, P. Vranas &
"QCDSP: Design, Performance and Cost", ACM/IEEE SC97, 1998.
D. Chen, N. Christ, Z. Dong, A. Gara, R. Mawhinney, S. Ohta,
T. Wettig, "QCDOC Architecture" Internal Report, Columbia
University, May 2000
"Simulation of a Computer Architecture for
Quantum Chromodynamics Calculations", S.R. Alam, R.N. Ibbett and F.
Mallet, Crossroads, The ACM Student Magazine, Interdisciplinary
Computer Science, Issue 9.3, Spring 2003, pp 16-23.
"A Methodology for Simulating Scientific
Supercomputing Systems", S. Alam and R.N. Ibbett, Summer Computer
Simulation Conference, USA, July 2004.
"Performance Evaluation of Local Communications: A
Case-study", S.R. Alam, R.N. Ibbett and F. Mallet, 15th
International Conference on Parallel and Distributed Computing and
Systems, IASTED, pp 393-398, USA, November 2003.
"An Extensible Clock mechanism for Computer
Architecture Simulations", F. Mallet, S. Alam and R.N. Ibbett,
Proc. 13th International Conference on Modelling and Simulation,
IASTED, USA, pp 91-96 May 2002.
"JavaHase: Automatic Generation of Applets from Hase
Simulation Models", F.Mallet and R.N. Ibbett, Proc. Summer Computer
Simulation Conference, Canada, July 2003, pp 659-664.
HASE models of QCDOC were developed at two different levels of
abstraction. The low-level model, which can simulate up to 16
processing nodes, captures the microarchitectural details of the
system, including the processor, the on-chip cache hierarchy, the
system bus, the communication unit, etc. This model was used to study
the performance characteristics of a single node and nearest neighbour
communications when executing QCD code.
In the high-level model, which can simulate up to 12K processing
nodes, the nodes simply act as sources of communication events, with
the intervals between events being based on data taken from the
low-level abstraction model. This model was used to study the
performance characteristics of the custom communication protocol and
different ways of implementing the QCD global sum mechanism.
More details of the models can be found at HASE
QCDOC Models (These pages are under construction).
Return to HASE home page
Institute for Computing Systems Architecture, School of Informatics,
University of Edinburgh
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