Architecture of Computing Systems (Lecture Notes in Computer ...

236 F. Xudong et al.
compared to the naive GPU version and obtains as high as 15.06x speedup versus
the CPU implementation run on an Intel Xeon E5405 CPU.
The remainder of this paper is arranged as follows: Section 2 describes the background
information of programming with Brook+ on AMD Radeon HD4870. Section
3 illustrates our optimization strategies. Section 4 evaluates the effectiveness
of the strategies. Section 5 discusses related work and the final section states our
conclusions.
2 Background
Using GPUs and general purpose CPUs to construct heterogeneous parallel systems
has attracted much interest in the field of high performance computing (HPC)
[5]. GPUs’ powerful floating-point operation capacity and high performance-perwatt
qualify them as good accelerators to speedup CPU applications for high performance
with relatively small system scale and low power consumption. In this
section, we introduce some background information concerning programming on
an AMD GPU platform using Brook+, including the micro architecture of Radeon
HD4870 GPU and the Brook+ stream programming environment.
2.1 Micro Architecture
In this paper, we use an AMD Radeon HD4870 GPU as the accelerator for
the CPU. AMD’s HD4800 series (codename RV770) is the newest GPU in their
stream computing lineup which supports double precision floating point operations.
The RV770 core has 10 SIMD engines, each of which contains 16 thread
processors. Each thread processor consists of five scalar stream cores. So there
are in total 800 cores integrated on a single die. The five cores can execute both
single-precision floating point and integer operations, with one of them being
able to handle transcendental operations, such as sin, cos, and log. Notably, a
thread processor combines four of its stream cores (excluding the transcendental
one) to process double-precision operations. In addition, a branch execution
unit is contained in each thread processor to handle branch executions. Tab. 1
summarizes the HD4870’s specifications.
In the AMD stream computing model, a stream denotes a collection of data
elements of the same type that can be operated on in parallel. A kernel is a
parallel function that operates on each element of an output stream. An instance
of kernel execution on a thread processor is called a thread. Threads
are mapped to thread processors for execution and scheduled in wavefronts. A
Table 1. AMD’s HD4870 Specification
Thread Processors 800 Memory Clock Speed 993 MHz
Texture Units 40 Memory Interface 256 bits
Core Clock Speed 750 MHz Memory Bandwidth 115 GB/s
Memory Type GDDR5 Single (Double) Peak 1.2 T (240G) flops