电子工程代写|计算机系统结构代写Computer Systems Architecture代考|CS1533

电子工程代写|计算机系统结构代写Computer Systems Architecture代考|Discussion and Conclusion

The stick pulling experiment clearly indicates the tradeoff between creating chances to collaborate and ensuring that resources are not depleted. Each stick site can be seen as a resource that needs to be populated, because if they are underused the system performance suffers. However, the resource ‘space’ between the sites is limited. Hence, we find an optimum system size that balances the use of stick sites and space.

The parallel optimization experiment indicates the tradeoff between collaborating while not loosing too much diversity. If there is no collaboration, each robot independently tries to optimize the problem. If each robot is connected to every other robot, then the search is not parallelized anymore but all robots investigate the same problem instances in parallel. There is clearly an optimum between sharing some information (a medium information flow through the system) and sharing too much information.

Gunther’s interpretation of his Universal Scaling Law speaks of contention (i.e., overhead in sharing resources) and lack of coherence (e.g., as in cache hierarchies). While contention can be easily identified in the multi-robot setup (e.g., for linearly scaled commuting times in the stick pulling scenario, see Fig. 4(b)), a correspondence to ‘lack of coherency’ is difficult to be identified. Instead we see two contradicting uses of shared resources in the stick pulling scenario. One resource is supposed to be populated to increase profit (stick sites) but the other resource is already depleted and creates overheads (space). In the parallel optimization scenario, there is also no lack of coherence but instead a too intensive communication that then crucially reduces exploration in the system.

Superlinearity seems more frequent in multi-robot systems and swarm systems probably mainly due to physical effects. In tasks, such as collectively pulling a heavy object and passing a gap or a steep hill, one or a few robots basically achieve zero performance (they cannot pull the object at all due to friction, they can just not pass the gap or the hill) but once a certain threshold $N_{c}$ of system size $N>N_{c}$ is reached the performance increases rapidly. Superlinearity as seen in the stick pulling scenario, however, is more subtle and less easily connected directly to such a single cause. Obviously it is the interplay of not underusing one resource while not depleting another.

电子工程代写|计算机系统结构代写Computer Systems Architecture代考|Basic Fingerprinting

During the execution of an application, a flow of instructions is executed. This flow is not homogeneous in terms of type of instructions, source of the instructions, and execution time of instructions. Accordingly, measuring for example the number of executed floating point instructions per time unit will lead to a characteristic curve of an application or a part of the application. If the application is executed several times with the same input parameters the measured curves are very similar (if sample rates greater than $1 \mu$ are applied). For tracking the progress of a known application, its measured curve can be compared to the recorded reference curve.

In case an application executed on a multicore processor suffers from interferences with other applications on the shared memory hierarchy, its progress is slowed down. Slowing down the application will result in a stretched (in time) but shrunk (in the value range) curve. When comparing such a mutated measured curve with the original reference curve, the actual slowdown can not only be identified but also be quantified at any time during execution.

Many current MPSoC (e.g. based on ARM, PowerPC) include performance counters implemented in hardware which can be configured to increment every time a given event is raised. While the amount of events which can be configured is usually more than 100 , the amount of counters that can be incremented simultaneously is small (around 4 to 6) [16]. An example of such curves is shown in Fig. $2 .$

The Fingerprint model is obtained by the execution of the main application several (thousand) times without other applications running in parallel. The performance counter values of the selected events are recorded with the frequency defined by the safety net system ( $100 \mu$ s period in the prototype FPGA case). Afterwards, the recorded characteristics are clustered in order to reduce the amount of curves that are combined into a model.

电子工程代写|计算机系统结构代写Computer Systems Architecture代考|Discussion and Conclusion

Gunther 对他的 Universal Scaling Law 的解释谈到了争用（即共享资源的开销）和缺乏连贯性（例如，在缓存层次结构中）。虽然在多机器人设置中可以很容易地识别出争用（例如，对于拉杆场景中的线性缩放通勤时间，参见图 4（b）），但很难识别与“缺乏一致性”的对应关系。相反，我们在拉杆场景中看到了共享资源的两种相互矛盾的用途。一种资源应该被填充以增加利润（粘性站点），但另一种资源已经耗尽并产生开销（空间）。在并行优化场景中，也不缺乏一致性，而是过于密集的通信，这会严重减少系统中的探索。

电子工程代写|计算机系统结构代写Computer Systems Architecture代考|Basic Fingerprinting

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