P. Puschner and A. Schedl. Computing Maximum Task Execution Times -- A Graph--Based Approach. Real--Time Systems, 13(1):67--91, 1997.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....explicitly explore the execution paths of a program fragment [16, 24] They can handle complex flow constraints somewhat better. The Implicit Path Enumeration Technique (IPET) finally, models possible program flows for (possibly unstructured) control flow graphs with arithmetic constraints [19, 22]. Each entity i in the graph is given an execution time t i by the low level analysis. The WCET is estimated by max( i x i t i ) where x i is an execution count for entity i, subject to the constraints on program flow given by the flow analysis and the program flow graph. If these constraints ....

....linear programming algorithm to solve the ILP problem. The Parametric Integer Programming algorithm benefits directly from this, since it uses the dual simplex method as the first step. This observation also applies to conventional, non parametric IPET. IPET problems considered in the literature [19, 22] often have linear constraints with other coefficients. These typically arise from loops, encoding statements like the loop body always executes at most c times the execution count of the basic block preceding the loop . This is a way to express an upper loop count bound c relative the ....

P. Puschner and A. Schedl. Computing maximum task execution times -- a graphbased approach. Journal of Real-Time Systems, 13(1):67--91, Jul. 1997.

....ubiquitous systems with real time constraints it is required to specify the timing constraints in the interface of each component. Analysis techniques like worst case execution time (WCET) respectively best case execution time (BCET) analysis have to be used to guarantee correct timing behaviour [2, 4]. The CVM service has to detect contractions in the timing requirements of di#erent components. The consequence on not fullfilling these requirements could be refusal of certain components for integration. For high dependable systems that are required to use such a component in its operation, the ....

P. Puschner and A. V. Schedl. Computing Maximum Task Execution Times -- A GraphBased Approach. The Journal of Real-Time Systems, 13:67--91, 1997.

....along the worst of these paths. ii) execution time for each atomic unit of a path has to be accurately estimated. There are two ways to determine what sequence of instructions will be executed. On the one hand, it is possible to consider all paths implicitly by using integer linear programming [10, 20, 15]. On the other hand, the enumeration of program paths can be explicit as in tree based methods [17, 12, 3] Some information is either required or useful to tighten path description: how many times loops iterate, dependencies between if statements, etc. This information can be user provided ....

P. Puschner and A. V. Schedl. Computing maximum task execution times - a graph based approach. In Proc. of IEEE Real-Time Systems Symposium, volume 13, pages 67-91. Kluwer Academic Publishers, 1997.

....local IFS 2 Fig. 8: Communication and computation instants among three nodes is the worst case execution time of the control application. To obtain the worst case execution time we plan to use a tool for static WCET analysis like CALC WCET 167 [17] The tool uses a graph based approach [18] to derive a safe upper bound for the execution of a code piece written in WCETC. The language is an extension to C, that needs some annotations for loop bounds, etc. Given that the necessary timing constraints can be satisfied, the sensor fusion process is transparent to the control application ....

P. Puschner and A. Schedl. Computing maximum task execution times -- a graphbased approach. Journal of Real-Time Systems, 13(1), July 1997.

....along the worst of these paths. ii) execution time for each atomic unit of a path has to be accurately es timated. There are two ways to determine what sequence of instructions will be executed. On the one hand, it is possible to consider all paths implicitly by using integer linear programming [10, 19, 14]. On the other hand, the enumeration of program paths can be explicit as in tree based methods [16, 12, 2] Some information is either required or useful to tighten path description: how many times loops iterate, dependencies between if statements, etc. This information can be user provided ....

P. Puschner and A. V. Schedl. Computing maximum task execution times a graph based approach. In Proc. oflEEE Real-Time Systems Symposium, volume 13, pages 67 91. Kluwer Academic Publishers, 1997.

....guarantees on the schedulability of the system, such as Rate Monotonic Analysis (RMA) 5] 1] rely on the estimation of the worst case execution times of the different tasks and actions that execute in the system. Although there are techniques to measure or calculate these execution times [9][10], this is always a difficult task because of the unpredictability of the different execution paths within the program. Today s computer architectures with superscalar processors [11] and caches [8] make the prediction of execution times even more difficult, specially in the context of concurrent ....

P. Puschner and A.V. Schedl. "Computing Maximum Task Execution Times: A graphbased approach". Real-Time Systems Journal, Vol. 13, No. 1, pp. 67-91, July 1997.

....extracted and all sorts of data dependencies established, in a very similar way as they could be extracted from high level languages. One of the principal problems in WCET is determining loops, and bounding the number of times each loop can execute. Several techniques exist for such purpose [12]. Two approaches are possible. To automatically extract and detect loops bounds and or rely on information provided by the programmer to bound the number of loop iterations. In any case, there are some loops for which no automatic tool can extract maximum execution times and therefore annotations ....

....context tree graph. The timing model of the virtual machine is used to time each basic block. Finally, a technique to compute the WCET of the resulting graph (i.e. graph collapsing for simple models or integer linear programming techniques for more complex graphs) is used to determine the WCET [12]. The latest status of the tool can be obtained from http: www.cs.york.ac.uk bernat javelin.html We are currently developing a timing model of the LORCAS Virtual Machine which has been developed at the University of York. This will complete the development of a portable code infrastructure based ....

P. Puschner and A. B. Schedl. Computing maximum task execution times - a graph based approach. Real-Time Systems, 1(27), 1991.

....[KU76, KU77] and a large number of algorithms has been developed (cf. e.g. AC76, GW76, HU77, Sre95, SGL98, Tar81a, Tar81b] See [MR90, RP86] for an overview. Worst Case Execution Time (WCET) analysis does not have such a long standing tradition (cf. e.g. CBW96, HS91, ITM90, NP93, Par93, PK89, PS97, Sha89] Designers of real time programming languages usually restrict language features in order to make it possible to guarantee time bounds and introduce new language features to let the programmer add extraneous information on the algorithms which cannot be determined from the source code. ....

....features. These constructs are scopes, markers, and loop sequences. Markers are used to define the number of loop iterations if this number cannot be estimated from the program automatically, e.g. if a general loop is used. Nevertheless all loops are forced to have a constant upper bound. 6. In [PS97] an integer linear programming approach (similar to that of [LM95] is employed, which together with so called T graphs is used to determine the WCET of real time programs. A T graph is similar to a control flow graph (CFG) of a program. In fact, a T graph is dual to its corresponding CFG, which ....

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Peter Puschner and Anton V. Schedl, Computing maximum task execution times -- a graph-based approach, Real-Time Systems 13 (1997), no. 1, 67--91. 1, 2, 2, 32, 32

....(Marlowe and Ryder, 1990; Ryder and Paull, 1986) for an overview. Worst Case Execution Time (WCET) analysis does not have such a long standing tradition (cf. e.g. Chapman et al. 1996; Halang and Stoyenko, 1991; Ishikawa et al. 1990; Nirkhe and Pugh, 1993; Park, 1993; Puschner and Koza, 1989; Puschner and Schedl, 1997; Shaw, 1989) Designers of real time programming languages usually restrict language features in order to make it possible to guarantee time bounds and introduce new language features to let the programmer add extraneous information on the algorithms which cannot be determined from the source ....

....features. These constructs are scopes, markers, and loop sequences. Markers are used to define the number of loop iterations if this number cannot be estimated from the program automatically, e.g. if a general loop is used. Nevertheless all loops are forced to have a constant upper bound. 6. In (Puschner and Schedl, 1997) an integer linear programming approach (similar to that of (Li and Malik, 1995) is employed, which together with so called T graphs is used to determine the WCET of real time programs. A T graph is similar to a control flow graph (CFG) of a program. In fact, a T graph is dual to its ....

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Puschner, P. and A. V. Schedl: 1997, `Computing Maximum Task Execution Times -- A Graph-Based Approach'. Real-Time Systems 13(1), 67--91.

....1 assignments, we need to apply data flow analysis to each possible control flow path [4] In each of these applications it is important that we can eliminate those paths that will never be followed at run time. In the literature, such paths are often referred to as false [8] or infeasible [16]. Here we favour the term dead [5] which avoids confusion with the (related but different) predicate transformer notion of infeasibility [13, p. 11] Applying analysis techniques to dead paths wastes time and effort. More seriously, though, apparent errors detected in dead paths during, for ....

....explicitly indicate which paths are dead or, conversely, which paths are possible. For instance, Park [14] defines a path language in which regular expressions over statement labels can be used to explicitly describe possible control flow paths. Similarly, Li et al. 11] and Puschner and Schedl [16] allow the programmer to provide integer linear constraint equations based on how many times each statement label is expected to be passed. A similar capability is achieved by Chapman et al. 5] who allow mode annotations in the source program to explicitly state under what circumstances a ....

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P. P. Puschner and A. V. Schedl. Computing maximum task execution times: A graph-based approach. Real-Time Systems, 13(1):67--91, July 1997.

....section surveys related work, which is followed by a short description of the environment we are working with. In Section 4 our approach is presented in detail. A summary of the results is given before we indicate future work in the last section. 2 Related Work Puschner and Schedl describe in [14] an approach where the control flow graph is analyzed to gain knowledge of the worst case execution path of a program. In contrast to our work, the execution time of basic blocks is assumed to be known. A linear programming approach is taken to compute the worst case execution path and therefore ....

P. Puschner and A. v. Schedl. Computing maximum task execution times --- a graph--based approach. Journal of Realtime Systems, pages 67--91, July 1995.

....the minimum invocation period and the maximum execution times of hard real time activities must be known. This implies that only periodic and sporadic activities may have hard deadlines. There are mature research results, which enable the calculation of the maximum execution time of tasks [13] [14], and the generation of a feasible offline schedule [3] assuming a TDMA protocol on the system T4 T1 T3 T2 T 5 T6 T7 M1 M2 M3 M4 M 5 M 6 M 7 Initiating event (Stimulus) Resulting event (Response) Figure 1. A real time transaction consisting of tasks and messages bus. By using these methods, ....

....At the ready time t o of the beginning task of a realtime transaction A, the laxity L A (t o ) is estimated as d A t o MET A , where d A is the deadline of A, and MET A is the maximum execution time of A. MET A can be calculated at the design time, by applying the method described in [14] at a higher level, based on the maximum execution times of tasks and maximum transmission times of messages (including the anticipated time redundancy) and the graph representation of A (cf. Figure 1) According to this scheme, soft real time messages are scheduled by EDF, which is known to be ....

P. Puschner and A. Schedl, "Computing Maximum Task Execution Times -- A Graph-Based Approach", J. Real Time Systems 13(1):67-91, 1997.

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P. Puschner and A. V. Schedl. Computing Maximum Task Execution Times -- A Graph-Based Approach. The Journal of Real-Time Systems, 13:67--91, 1997. 6

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Peter Puschner and Anton V. Schedl. Computing Maximum Task Execution Times A Graph-Based Approach. The Journal of Real-Time Systems, 13:6791, 1997.

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Peter Puschner and Anton V. Schedl. Computing Maximum Task Execution Times -- A Graph-Based Approach. The Journal of Real-Time Systems, 13:67--91, 1997.

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P. Puschner and A. V. Schedl. Computing Maximum Task Execution Times -- A Graph-Based Approach. The Journal of Real-Time Systems, 13:67--91, 1997.

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P. Puschner and A. V. Schedl. Computing Maximum Task Execution Times -- A Graph-Based Approach. The Journal of Real-Time Systems, 13:67--91, 1997.

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P. Puschner and A. Schedl. Computing Maximum Task Execution Times --- A Graph-Based Approach. Real-Time Systems, 13(1):67--91, July 1997.

....corresponding JCF and used by the WCET tool. The WCETAn class is language independent, Java and Ada versions have already been produced [4] It allows scopes or code block boundaries, maximum number of iterations of loops, execution modes and arbitrary path execution frequencies to be described [8]. Take the following code example. which shows how to specify that a loop iterates 50 times in the worst case, but that in the particular mode of operation called quick mode it only iterates 10 times. WCETAn.mode quick mode = new WCETAn.mode( WCETAn.LoopCount (50) WCETAn.LoopCoount ....

P. Puschner and A. Schedl, "Computing maximum task execution times - a graph based approach," Real-Time Systems, vol. 13, pp. 67--91, July 1997.

....4.1.2 Frequency Relations Frequency relations describe execution frequency bounds of single program parts and express disjunctive sets of linear relations between the execution frequencies of two or more program parts. Frequency relations implement the relative frequency constraints described in [Puschner, Schedl 1997]. Frequency relations are linear equations or inequalities. They characterize the execution frequencies of program parts marked with the marker construct: MARKER(name) The argument name is the unique name of the marker. In frequency relations marker names are used to describe the frequencies of ....

P. Puschner and A. Schedl. Computing Maximum Task Execution Times --- A Graph-Based Approach. Real-Time Systems, 13(1):67--91, July 1997.

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P. Puschner and A. Schedl. Computing Maximum Task Execution Times -- A Graph--Based Approach. Real--Time Systems, 13(1):67--91, 1997.

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P. Puschner and A. Schedl. Computing maximum task execution times --- a graph-based approach. Journal of Real-Time Systems, to appear.

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P. Puschner and A. V. Schedl. Computing Maximum Task Execution Times -- A Graph-Based Approach. The Journal of Real-Time Systems, 13:67--91, 1997.

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P. Puschner. Computing maximum task execution times -- a graph-based approach. Real-Time Systems, 9(4), Oct. 1997.

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P. Puschner, and A. Schedl. Computing Maximum Task Execution Times --- A Graph-Based Approach, Real-Time Systems, Kluwer Academic Publishers, volume 13, number 1, pages 6791, July 1997.

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