calc_delta_fair
vprot = min_vruntime(vprot, se->vruntime + calc_delta_fair(slice, se));
se->vprot = min_vruntime(se->vprot, se->vruntime + calc_delta_fair(slice, se));
se->deadline = se->vruntime + calc_delta_fair(se->slice, se);
curr->vruntime += calc_delta_fair(delta_exec, curr);
vslice = calc_delta_fair(se->slice, se);
limit = calc_delta_fair(max_slice, se);