Use of cumulatives

I'm working on a problem where I use the `cumulatives/[2,3]` predicate. But I get very bad performance when I try to combine this with `minimize` in `labeling` I have the following demo. 10 task, all with duration 1, 4 machines, all with capacity=1. My goal is to minimize the total time, i.e. `minimize(maximum(Es))`: ``` :- use_module(library(clpfd)). :- use_module(library(lists)). go( Ss, Es, Ms, Tm, Lab ) :- Ss = [S1, S2, S3, S4,S5,S6,S7,S8,S9,S10], %Starttimes Es = [E1, E2, E3, E4,E5,E6,E7,E8,E9,E10], %Endtimeds Ms = [M1, M2, M3, M4,M5,M6,M7,M8,M9,M10], %MachineIds domain(Ss, 1, 20), domain(Es, 1, 20), domain(Ms, 1, 10), %All task has duration = 1 Tasks = [ task( S1, 1, E1, 1, M1 ), task( S2, 1, E2, 1, M2 ), task( S3, 1, E3, 1, M3 ), task( S4, 1, E4, 1, M4 ), task( S5, 1, E5, 1, M5 ), task( S6, 1, E6, 1, M6 ), task( S7, 1, E7, 1, M7 ), task( S8, 1, E8, 1, M8 ), task( S9, 1, E9, 1, M9 ), task( S10, 1, E10, 1, M10 ) ], %All machines has resource capacity = 1 Machines = [ machine( 1, 1 ), machine( 2, 1 ), machine( 3, 1 ), machine( 4, 1 ) ], cumulatives(Tasks, Machines, [bound(upper)] ), maximum( MaxEndTime, Es ), %Make the list of options to pass to the labeling predicate append( [ [minimize(MaxEndTime)], [time_out( Tm, _)], Lab ], LabOpt ), %The variables to lable: append([Ms, Ss ], Vars), labeling( LabOpt, Vars). ``` If I now run this and solve for 1 second I get: ``` | ?- go( S, E, M, 1000, []). E = [2,3,4,5,6,7,8,9,10,11], M = [1,1,1,1,1,1,1,1,1,1], S = [1,2,3,4,5,6,7,8,9,10] ? ``` I.e. all tasks has been scheduled to run on machine 1 I need to run the solver for 30 second before I see any sign of minimization: ``` | ?- go( S, E, M, 30000, []). E = [2,3,4,5,6,7,8,9,10,2], M = [1,1,1,1,1,1,1,1,1,2], S = [1,2,3,4,5,6,7,8,9,1] ? ``` If I run for 60 second I start to get acceptable results: ``` | ?- go( S, E, M, 60000, []). E = [2,3,4,2,3,4,2,3,4,2], M = [1,1,1,2,2,2,3,3,3,4], S = [1,2,3,1,2,3,1,2,3,1] ? ``` I feel that this is taking way too long time. Any comments on why it takes so long time?