As the complexity of system design increases, use of pre-designed components, such as generalpurpose microprocessors, provides an effective way to reduce the complexity of synthesized hardware. While the design problem of systems that contain processors and ASIC chips is not new, computeraided synthesis of such heterogeneous or mixed systems poses challenging problems because of the differences in model and rate of computation by application-specific hardware and processor software. In this article, we demonstrate the feasibility of achieving synthesis of heterogeneous systems which uses timing constraints to delegate tasks between hardware and software such that the final implementation meets required performance constraints. 1

Abstract|As both the number of processors and the complexity of problems to be solved increase, programming multiprocessing systems becomes more di cult and error-prone. This paper discusses programming assistance and automation concepts and their application to a program development tool for message-passing systems called Hypertool. It performs scheduling and handles the communication primitive insertion automatically. Two algorithms, based on the critical-path method, are presented for scheduling processes statically. Hypertool also generates the performance estimates and other program quality measures to help programmers in improving their algorithms and programs. I.

Devices]: Modes of Computation---Parallelism and concurrency General Terms: Algorithms, Design, Performance, Theory Additional Key Words and Phrases: Automatic parallelization, DAG, multiprocessors, parallel processing, software tools, static scheduling, task graphs This research was supported by the Hong Kong Research Grants Council under contract numbers HKUST 734/96E, HKUST 6076/97E, and HKU 7124/99E. Authors' addresses: Y.-K. Kwok, Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong; email: ykwok@eee.hku.hk; I. Ahmad, Department of Computer Science, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong. Permission to make digital / hard copy of part or all of this work for personal or classroom use is granted without fee provided that the copies are not made or distributed for profit or commercial advantage, the copyright notice, the title of the publication, and its date appear, and notice is given that copying is by permission of the ACM, Inc. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and / or a fee. 2000 ACM 0360-0300/99/1200--0406 $5.00 ACM Computing Surveys, Vol. 31, No. 4, December 1999 1.

Abstract Multiprogrammed multiprocessors executing fine-grained parallel programs appear to require new scheduling policies. A promising new idea is gang scheduling, where a set of threads are scheduled to execute simultaneously on a set of processors. This has the intuitive appeal of supplying the threads with an environment that is very similar to a dedicated machine. It allows the threads to interact efficiently by using busy waiting, without the risk of waiting for a thread that currently is not running. Without gang scheduling, threads have to block in order to synchronize, thus suffering the overhead of a context switch. While this is tolerable in coarse grain computations, and might even lead to performance benefits if the threads are highly unbalanced, it causes severe performance degradation in the fine-grain case. We have developed a model to evaluate the performance of different combinations of synchronization mechanisms and scheduling policies, and validated it by an implementation on the Makbilan multiprocessor. The model leads to the conclusion that gang scheduling is required for efficient fine grain synchronization on multiprogrammed multiprocessors. 1 Introduction Multiprocessors are often dedicated to running a single application at a time. The program is allowed full control over what happens on each processor, and in fact it might be required to include instructions that regulate the mapping and scheduling of parallel threads. Much experience relating to these issues has been accumulated over the years, and automatic parallelization and compilation techniques have been developed. These techniques allow dedicated processors to be used efficiently by a single application.

This paper describes the design and implementation of an optimizing compiler that automatically generates profile information to assist classic code optimizations. This compiler contains two new components, an execution profiler and a profile-based code optimizer, which are not commonly found in traditional optimizing compilers. The execution profiler inserts probes into the input program, executes the input program for several inputs, accumulates profile information and supplies this information to the optimizer. The profile-based code optimizer uses the profile information to expose new optimization opportunities that are not visible to traditional global optimization methods. Experimental results show that the profile-based code optimizer significantly improves the performance of production C programs that have already been optimized by a high-quality global code optimizer

In this paper, we propose a static scheduling algorithm for allocating task graphs to fullyconnected multiprocessors. We discuss six recently reported scheduling algorithms and show that they possess one drawback or the other which can lead to poor performance. The proposed algorithm, which is called the Dynamic Critical-Path (DCP) scheduling algorithm, is different from the previously proposed algorithms in a number of ways. First, it determines the critical path of the task graph and selects the next node to be scheduled in a dynamic fashion. Second, it rearranges the schedule on each processor dynamically in the sense that the positions of the nodes in the partial schedules are not fixed until all nodes have been considered. Third, it selects a suitable processor for a node by looking ahead the potential start times of the remaining nodes on that processor, and schedules relatively less important nodes to the processors already in use. A global as well as a pair-wise comparison is c...

This paper addresses the problem of compiling perfectly nested loops for multicomputers (distributed memory machines). The relatively high communication startup costs in these machines renders frequent communication very expensive. Motivated by this, we present a method of aggregating a number of loop iterations into tiles where the tiles execute atomically -- a processor executing the iterations belonging to a tile receives all the data it needs before executing any one of the iterations in the tile, executes all the iterations in the tile and then sends the data needed by other processors. Since synchronization is not allowed during the execution of a tile, partitioning the iteration space into tiles must not result in deadlock. We first show the equivalence between the problem of finding partitions and the problem of determining the cone for a given set of dependence vectors. We then present an approach to partitioning the iteration space into deadlock-free tiles so that communicati...

Symbolic Domain The objects in our abstract symbolic domain are canonical symbolic expressions. A canonical symbolic expression is a lexicographically ordered sequence of symbolic terms. Each symbolic term is in turn a pair of an integer coefficient and a sequence of pairs of pointers to program variables in the program symbol table and their exponents. The latter sequence is also lexicographically ordered. For example, the abstract value of the symbolic expression 2ij+3jk in an environment that i is bound to (1; (( " i ; 1))), j is bound to (1; (( " j ; 1))), and k is bound to (1; (( " k ; 1))) is ((2; (( " i ; 1); ( " j ; 1))); (3; (( " j ; 1); ( " k ; 1)))). In our framework, environment is the abstract analogous of state concept; an environment is a function from program variables to abstract symbolic values. Each environment e associates a canonical symbolic value e x for each variable x 2 V ; it is said that x is bound to e x. An environment might be represented by...

This paper presents a general framework for determining average program execution times and their variance, based on the program's interval structure and control dependence graph. Average execution times and variance values are computed using frequency information from an optimized counter-based execution profile of the program. 1 Introduction It is important for a compiler to obtain estimates of execution times for subcomputations of an input program, if it is to attempt optimizations related to overhead values in the target architecture. In earlier work [SH86a, SH86b, Sar87, Sar89], we used estimates of execution times to facilitate the automatic partitioning and scheduling of programs written in the singleassignment language, Sisal, for parallel execution on multiprocessors. In this paper, we present a general framework for estimating average execution times in a program. This approach is based on the interval structure [ASU86] and the control dependence relation [FOW87], both of w...

High Performance Fortran (HPF) has emerged as a standard dialect of Fortran for data parallel computing. However, for a wide variety of applications, both task and data parallelism must be exploited to achieve the best possible performance on a multicomputer. We present the design and implementation of a Fortran compiler that integrates task and data parallelism in an HPF framework. A small set of simple directives allow users to express task parallel programs in a variety of domains. The user identifies opportunities for task parallelism, and the compiler handles task creation and management, as well as communication between tasks. Since a unified compiler handles both task parallelism and data parallelism, existing data parallel programs and libraries can serve as the building blocks for constructing larger task parallel programs. This paper concludes with a description of several parallel application kernels that were developed with the compiler. The examples demonstrate that exploi...