Software pipelining modulo scheduling

Software pipelining of loops by the method of modulo scheduling. Enhanced coscheduling a software pipelining method using. Creating software pipelines lots of software pipelining techniques out there modulo scheduling most widely adopted practical to implement, yields good results conceptual strategy unroll the loop completely then, schedule the code completely with 2 constraints. It is important to distinguish software pipelining, which is a target code technique for overlapping loop iterations, from modulo scheduling, the currently most.

Lam computer systems laboratory stanford university abstract the basic idea behind software pipelining was. Modulo scheduling is a framework within which algorithms for the software. Exploiting vector parallelism in software pipelined. As instructionlevel parallelism made its way into generalpurpose computing, it. It is well known that, as a rule, there is inadequate. Software pipelining often modulo scheduling i interleave operations from multiple loop iterations i improved loop ilp i currently missing from llvm i loop scheduling technique i requires both loop dependency and resource availability information i usually done at a target speci c level as part of scheduling i but it would be very good if we. Software pipelining has been known to assembly language programmers of machines with instructionlevel parallelism since such architectures existed. Only a relatively small number of intervals need to be considered, since an upper bound on the initiation interval is the length of the unscheduled loop body and a lower bound is the longest loopcarried dependency. Softwarepipelining is a loop scheduling technique aimed at increasing the instruction level parallelism by scheduling operations from di erent loop iterations in an overlapping fashion. Algorithms for achieving software pipelining fall into two broad classes. Basic instruction scheduling and software pipelining. Box 850118, richardson, texas 750850118, usa software pipelining is a. This paper presents a novel software pipelining approach, which is calledswing modulo scheduling sms.

While a variety of modulo scheduling algorithms exist for software pipelining, they are not amenable to many complex design constraints and optimization goals that arise in the hardware synthesis context. This paper presents a practical algorithm, iterative modulo scheduling, that is capable of dealing with realistic machine models. A comparison of modulo scheduling techniques for software. Modulo scheduling ms 34 is a software pipelining technique which overlaps different iterations of a loop to exploit a higher degree of instructionlevel parallelism ilp. Most commonly, softwarepipelining is implemented through a technique called modulo scheduling 2, 4, 6, 9. Only a relatively small number of intervals need to be considered, since an upper bound on the initiation interval is the length of the unscheduled loop. Predicateaware, makespanpreserving software pipelining of. This paper presents the results of an experimental evaluation and comparison of different scheduling algorithms that generate software pipelines. The same color is used to outline the source and destination of forwarding. Software pipelining 9 ld alu st ld alu st ld alu st ld alu st iteration 1 iteration 2 iteration 3 iteration 4 t2 me ld alu st. Ramakrishna rau compiler and architecture research hpl94115 november, 1995 modulo scheduling, instruction scheduling, software pipelining, loop scheduling modulo scheduling is a framework within which algorithms for the software pipelining of innermost loops may be defined. Microprocessing and microprogramming 37 1993 99104 northholland 99 an extended scheduling technique for software pipelining dagung lua and prasenjit biswasb adeparlment of computer science and engineering, southern methodist university, dallas, texas 75275, usa bmicroprocessor architecture group, cyrix corporation, p. Software pipelining, as addressed here, is the problem of scheduling the operations within an iteration, such that the iterations can be pipelined to yield optimal throughput, software pipelining has also been studied under different con texts. Iterative modulo scheduling combines list scheduling, backtracking, and a modulo reservation table to reorder instructions from.

An algorithm for software pipelining loops, which appeared at micro 1994, 22 years before receiving the award. In our approach, by construction, it is the same in both the nonpipelined and pipelined scheduling tables. It is important to distinguish software pipelining, which is a target code technique for overlapping loop iterations, from modulo scheduling, the currently most effective known compiler technique for generating software pipelined loops. Software pipelining is an efficient method of loop optimization that allows for parallelism of operations related to different loop iterations. Since there are readafterwrite register dependencies raw. Software pipelining moduloscheduling software pipelining. Software pipelining is a technique that reforms the loop so that a faster execution rate is realized. Modulo scheduling is a framework within which a wide variety of algorithms and heuristics may be defined for software pipelining innermost loops. Pipelining aims to expose instruction level parallelism in loops which tend to help scientific and graphical applications. Sdcbased modulo scheduling for pipeline synthesis ieee. Software pipelining by modulo scheduling was originally envisioned for vliw machines where functional units must be statically scheduled to provide maximum utilization. Section 1 introduces terms common to many techniques.

A highlevel implementation of software pipelining in llvm. Software pipelining aims to expose instruction level parallelism in loops which tend to help scienti. Currently, most commercial compilers use loop pipelining methods based on modulo scheduling algorithms. The blue color is used to indicate the technique to perform the register file reads in. The software pipelining technique used by the st200 lao instruction scheduler to solve the pipeline instruction scheduling problem pisp is insertion scheduling, and a variant of modulo scheduling. An ability to identify, formulate and solve loops scheduling problems using 20080424 \course\cpeg42108s\topic7. Box 850118, richardson, texas 750850118, usa software pipelining is. In this paper, we propose a statediagram based approach for modulo scheduling or software pipelining, an instruction scheduling method for loops.

An extended scheduling technique for software pipelining. Modulo scheduling is a popular technique to enable pipelined execution of successive loop iterations for performance improvement. Static scheduling techniques local scheduling within a basic block loop unrolling software pipelining modulo scheduling trace scheduling predication ece 463521, profs. Our software pipelining algorithm is built from two components. Modulo sdc scheduling with recurrence minimization in high. This thesis details the implementation of swing modulo scheduling, a software pipelining technique, that is both e. Software pipelining has been known to assembly language programmers of machines with instructionlevel. A software pipelining method for generating a schedule for executing a plurality of instructions on a processor, the plurality of instructions involving one or more variables, the processor having one or more physical registers, the method comprising the step of scheduling each of the plurality of instructions, determining whether there is a variable for which there is less than a threshold. The software pipelining algorithms proposed by su et.

Move operations across iteration boundaries simplest technique. Modulo scheduling fill modulo reservation table better resource utilization, more ilp, also in the presence of loopcarried data. Register allocation and spilling via graph coloring, g. Swing modulo scheduling is an heuristic approach that has a low computational cost. Modulo scheduling was the first method proposed for loop pipelining or software pipelining. An algorithm for software pipelining loops, which appeared at micro. Loop scheduling and software pipelining 1 loop scheduling and software pipelining 2 reading list. Approaches to software pipelining iterative modulo scheduling similar to list scheduling, computes priorities and uses operation scheduling details later uses modulo reservation tables mrt a global resource reservation table with ii columns and r rows mrt records resource usage of the schedule of the kernel as it is constructed. A software pipelining method using moduloscheduled pipeline theory february 2000 international journal of parallel programming 281. Eecs 583 class 12 software pipelining modulo scheduling. Ability to apply knowledge of basic code generation techniques, e. Modulo scheduling is an approach for constructing software pipelines that focuses on minimizing the cycle count of the loops and thereby optimize performance. The most successful technique of software pipelining is known as the modulo scheduling 19. A dynamic modulo scheduling with binary translation.

Let abc n represent a loop containing operations a, b, c that is executed n times. It generates schedules that are near optimal in terms of initiation interval, register requirements and stage count. This paper also characterizes the algorithm in terms of the quality of the. Modulo scheduling fill modulo reservation table better resource utilization, more ilp, also in the presence of loopcarried data dependences c. Software pipelining is a wellknown and effective technique for generating compact loop schedules for instruction level parallel computers. Advanced compiler techniques tuesday, october 23th 2007. One of the bottlenecks toward an efficient fft implementation on these vliw dsp platforms is memory latencies. Ppt loop scheduling and software pipelining powerpoint. One common software pipelining heuristic is called iterative modulo scheduling ims 7, which has been adapted for loop pipelining in highlevel synthesis by pico 8, ctoverilog 9, and also by legup 10. Resourceconstrained software pipelining stanford cs theory. Iterative modulo scheduling combines listscheduling, backtracking, and a modulo reservation table to reorder instructions from. Instruction scheduling heuristic for an efficient fft in vliw. Software pipelining is a technique that improves the scheduling of instructions in loops by overlapping instructions from different iterations.

The body of the loop is repeatedly scheduled with different initiation intervals until a perfect schedule is reached, aikennicolau1988. Code generation schemes for modulo scheduled doloops and. We have proposed an efficient enumerationbased heuristic for modulo scheduling in 20. For ease of explanation, lets consider the simple 4instruction loop code depicted in fig. Iterative modulo scheduling ieeeacm international symposium. A software pipelining method using modulo scheduled pipeline theory february 2000 international journal of parallel programming 281. Code generation schemes for modulo scheduled doloops. Software pipelining is a loop scheduling technique which yields highly optimized loop schedules. Our approach adapts the classical pipeline theory for modulo scheduling, and, hence, the resulting theory is called moduloscheduled pipeline mspipeline theory. Iterations are executed in overlapped fashion to increase parallelism. Modulo scheduling for cgras is a logical extension with modulo counter control and a focus on inner loop parallelism. Our approach adapts the classical pipeline theory for modulo scheduling, and, hence, the resulting theory is called modulo scheduled pipeline mspipeline theory. An effective scheduling technique for vliw machines monica s.