This paper describes a new approach to experimentally estimate the application schedulability for various processor frequencies. We use additional workload generated by an artificial high priority routine to simulate the frequency decrease of a processor. Then we estimate the schedulability of applications at different frequencies. The results of such estimation can be used to determine the frequencies and control algorithms of dynamic voltage scaling/dynamic frequency scaling (DVS/DFS) implementations. The paper presents a general problem description, the proposed schedulability estimation method, its analysis and evaluation.