Method for scheduling a plurality of guest systems and/or threads in a system, the system comprising a virtualization system running on a processor , the virtualization system being adapted to assign processor time and memory space to the plurality of guest systems and comprising a virtualization system scheduler , the method including: - running a first guest system on the virtualization system , the first guest system comprising at least one first thread and at least one second thread running in the first guest system , and a guest system scheduler adapted to assign processing time to the at least one second thread , - assigning, in the virtualization system , a plurality of time reservations to the first guest system , wherein the plurality of time reservations include a first time reservation associated to the at least one first thread and a second time reservation associated to the guest system scheduler of the first guest system , - assigning processor time, by the virtualization system scheduler , to the first guest system according to the second time reservation, including: - providing, by the virtualization system scheduler , information to the first guest system, the information enabling to determine that the first thread has to be dispatched; - dispatching, by the virtualization system , the first guest system , and - dispatching, by a dispatcher of the first guest system, the at least one first thread in the first guest system ; and - assigning processor time, by the virtualization system scheduler , to the at least one first thread of the first guest system according to the first time reservation. - running a first guest system on the virtualization system , the first guest system comprising at least one first thread and at least one second thread running in the first guest system , and a guest system scheduler adapted to assign processing time to the at least one second thread , - assigning, in the virtualization system , a plurality of time reservations to the first guest system , wherein the plurality of time reservations include a first time reservation associated to the at least one first thread and a second time reservation associated to the guest system scheduler of the first guest system , - assigning processor time, by the virtualization system scheduler , to the first guest system according to the second time reservation, including: - providing, by the virtualization system scheduler , information to the first guest system, the information enabling to determine that the first thread has to be dispatched; - dispatching, by the virtualization system , the first guest system , and - dispatching, by a dispatcher of the first guest system, the at least one first thread in the first guest system ; and - providing, by the virtualization system scheduler , information to the first guest system, the information enabling to determine that the first thread has to be dispatched; - dispatching, by the virtualization system , the first guest system , and - dispatching, by a dispatcher of the first guest system, the at least one first thread in the first guest system ; - assigning processor time, by the virtualization system scheduler , to the at least one first thread of the first guest system according to the first time reservation. <EOS>