Method for scheduling a plurality of guest systems (22, 24) 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 (22, 24) 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 (44, 46) running in the first guest system, and a guest system scheduler adapted to assign processing time to the at least one second thread (44, 46), - 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 (68, 84) 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 (44, 46) running in the first guest system, and a guest system scheduler adapted to assign processing time to the at least one second thread (44, 46), - 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 (68, 84) 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 (68, 84) 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.