A typical approach for realizing digital controllers is to synthesize the control law in the continuous-time domain and then to implement it as a set of periodic threads complying with tight temporal constraints. The strict respect of all deadlines can often be obtained only by selecting low activation rates which determine a remarkable performance degradation. On the other hand, many control systems are known to tolerate a certain amount of deadline misses. We realized a software tool which allows to numerically evaluate the quality of the control resulting from the scheduling. The tool has been applied to a robotic case study. Considering a meaningful set of trajectories, we have drawn experimental evidence that the use of soft real-time constraints on the threads leads to significant improvements in the system performance. The performance improvement is more evident if scheduling approaches like resource reservation schemes, able to separate the thread importance from its activation rate, are used