*5.4.4 Experiment content*

In this section, the performance evaluation of the implemented **ABACsh** prototype in OpenStack is presented. Specifically, **ABACsh** policy engine which represents PDP of access control model is discussed. The experiments fall into three parts where the response time is calculated. Response time indicates the time consumed by the system in order to process the access request decision call. The response time has been used to measure the performance in several OpenStack implementations such as in [63, 64]. In these experiments, OpenStack cloud was installed in physical servers running Ubuntu 16.04 LTS release. Three types of execution time can be measured [65, 66]. The first one is real time that reflects the wall clock where the time is calculated from the start till the end of the call including the waiting time and time used by other processes. The second one is user-time that reflects the actual CPU-time spent outside the kernel during the process call in user-mode without considering other processes. The third one is sys-time that reflects the actual CPU-time spent within the kernel during the process execution.

Three experimental settings have been implemented as explained below.

