درک : تجسم رفتار سلسله مراتبی سیستم های زمان واقعی چند پردازنده

Trace visualization is a viable approach for gaining insight into the behavior of complex distributed real-time systems. Grasp is a versatile trace visualization toolset. Its flexible plugin infrastructure allows for easy extension with custom visualization and analysis techniques for automatic trace verification. This paper presents its visualization capabilities for hierarchical multiprocessor systems, including partitioned and global multiprocessor scheduling with migrating tasks and jobs, communication between jobs via shared memory and message passing, and hierarchical scheduling in combination with multiprocessor scheduling. For tracing distributed systems with asynchronous local clocks Grasp also supports the synchronization of traces from different processors during the visualization and analysis.

Modern real-time systems are becoming increasingly more complex, with many tasks executing concurrently on many processors, making it difficult to understand the system behavior. A popular trend in coping with the vast number of tasks and the resulting interferences between them is to hide tasks inside components and to integrate the system from those components. This approach requires hierarchical scheduling, which has been covered extensively in the literature for uniprocessor systems. Recently, the real-time literature has been investigating applying hierarchical scheduling to multiprocessor platforms. In this paper we address the problem of how to provide insight into complex interaction patterns between jobs executing in a hierarchical multiprocessor system. Several approaches are available for tackling the complexity of modern software systems. Ideally, every system would be meticulously documented, providing a formal yet concise description of the emergent system behavior. However, this is a long and costly process without immediate effects (such as additional functionality) and is therefore not common in practice. Examples of poorly documented code and system designs are abundant. The description of the dynamic system behavior therefore needs to be extracted from existing systems. There are modeling and verification tools available, which rely on the developers analyzing the implementation and constructing its model. These tools then employ formal methods to verify the behavior of the extracted model against an abstract model. The state of the art modeling and verification techniques, however, are not scalable and therefore can be applied to verify only a small portion of the entire system. Visualization tools offer an interesting alternative. Existing systems can be instrumented to generate runtime traces, which can then be analyzed by engineers and researchers, leveraging their expertise and human capacity to recognize patterns, to gain insight into the system behavior. The challenge here lies in representing and presenting the information in an intuitive way, enabling the user to extract the essential properties of the analyzed system. While trace visualization on its own is insufficient for the verification of timing constraints of a real-time system, it is well suited for early design of such systems before the formal validation stage is reached. Grasp is a toolset for tracing and visualizing the behavior of complex real-time systems. Its main strength lies in providing many different visualizations for various real-time primitives and scheduling techniques in a consistent and intuitive way. Its flexible architecture allows one to extend it easily with new visualization and analysis techniques. We have been using Grasp extensively within our group during our research on embedded real-time systems and the development of various extensions of a commercial real-time operating system μC/OS-II, including a hierarchical scheduling framework and slot shifting. The use of Grasp has also been reported in [1], [2] and [22] where it was used to gain insights into new approaches for hierarchical scheduling in Linux and VxWorks operating systems. Recently Grasp was used in the context of the SOFIA project to visualize the communication patterns between sensor nodes in a smart home environment. In this paper we focus on visualizing traces of multiprocessor systems. The challenge here lies in representing and presenting the execution and communication between jobs running on different processors in an intuitive and compact way. Moreover, if the timestamps of events occurring on a processor are recorded in its local time, special care must be taken to synchronize the individual traces. While some custom-built clusters such as IBM Blue Gene offer sufficiently accurate global clocks, most distributed systems can only rely on local clocks [3]. If the local clocks drift too far apart it may lead to inaccuracies or even errors during the trace analysis or visualization, as the causality between events may appear to be broken (e.g. messages arriving before they were sent).

Grasp is a visualization toolset aiming to provide insight into the behavior of complex real-time systems. Its flexible plugin infrastructure allows for easy extension with custom visualization and analysis techniques for automatic trace verification. In this paper we have presented its features for visualizing hierarchical multiprocessors scheduling. It provides various visualizations for partitioned and global multiprocessor scheduling with migrating tasks and jobs, communication between jobs via shared memory and message passing, and hierarchical scheduling in combination with multiprocessor scheduling. For tracing distributed systems with asynchronous local clocks Grasp also provides a simple interface which aids in synchronizing the individual traces during the visualization and analysis.