courseware Integer Linear Programming approach to Scheduling Sune Fallgaard Nielsen Informatics and Mathematical Modelling Technical University of Denmark Richard Petersens Plads, Building 322 DK2800 Lyngby, Denmark

SoC-MOBINET courseware[M-1] High-Level Synthesis2 Outline  Introduction - The new approach & objective - Automated data path synthesis  ILP Formulation  Example  Generalizations  Experimental Results  Conclusion

SoC-MOBINET courseware[M-1] High-Level Synthesis3 The New Approach  Solve scheduling problem 1) ASAP -> start time 2) ALAP -> require time 3) ILP (Integer Linear Programming)

SoC-MOBINET courseware[M-1] High-Level Synthesis4 Objective  Fully utilize the hardware resources i.e. minimize the requirement of function units under a given timing constraint

SoC-MOBINET courseware[M-1] High-Level Synthesis5 Support different kinds of data path  Multicycle operations  Multiple operations per cycle  Pipelined data paths  Mutually exclusive operations  Variables’ lifetime consideration

SoC-MOBINET courseware[M-1] High-Level Synthesis6 Automated Data Path Synthesis  Scheduling  Allocation  Tightly interdependent

SoC-MOBINET courseware[M-1] High-Level Synthesis7 Scheduling  ** very important  FIX 1) number & types of function units 2) lifetime of variables 3) timing constraints

SoC-MOBINET courseware[M-1] High-Level Synthesis8 The New Approach 1) ASAP 2) ALAP 3) ILP (Integer Linear Programming) Function Units:  Fully utilized  minimize maximal no.

SoC-MOBINET courseware[M-1] High-Level Synthesis9 The ILP Formulation 2 Assumptions:  Each operation – 1 cycle propagation delay  Consider non-pipelined data path

SoC-MOBINET courseware[M-1] High-Level Synthesis10 Data Flow Graph  n operations  s steps  o i – each operation 1 ≤ i ≤ n  o i  o j – precedence relation o i immediate predecessor of o j  m types of function units

SoC-MOBINET courseware[M-1] High-Level Synthesis11  S i – start time (ASAP)  L i – require time (ALAP)  C t i – cost of function unit of type t i (FU t i )  M t i – number of function unit of type t i  x i,j – 1: if o i is scheduled into step j 0: otherwise

SoC-MOBINET courseware[M-1] High-Level Synthesis12 Formulas (1,2)  Minimize total function unit cost O i Є FU t k for 1 ≤ j ≤ s, 1 ≤ k ≤ m  No control step should contain more than M t k function unit of type t k

SoC-MOBINET courseware[M-1] High-Level Synthesis13 Formulas (3,4)  o i can only be scheduled into a step between S i & L i for all o i  o k for 1 ≤ i ≤ n  Ensure the precedence relations of DFG will be preserved

SoC-MOBINET courseware[M-1] High-Level Synthesis14 Example  Available function units: ~ multipliers (FU t 1 ) ~ ALUs (FU t 2 )  Cost: ~ C t 1 = 5 ~ C t 2 = 1

SoC-MOBINET courseware[M-1] High-Level Synthesis15 Example  Integer programming formulation (formulas 1,2) minimize 5Mt 1 + Mt 2 O i Є FU t k

SoC-MOBINET courseware[M-1] High-Level Synthesis16 Example  Integer programming formulation (formulas 3,4) O 6  O 7 O 8  O 9 O 10  O 11

SoC-MOBINET courseware[M-1] High-Level Synthesis17 Example  Scheduling result -- optimal this formulation  variables x 1,1, x 2,1, x 3,2, x 4,3, x 5,4, x 7,3, x 8,3, x 9,4, x 10,1 & x 11,2 => 1  2 multipliers & 2 ALUs

SoC-MOBINET courseware[M-1] High-Level Synthesis18 Generalizations  Multicycle operations  Multiple operations per cycle  Pipelined data paths  Mutually exclusive operations  Variables’ lifetime consideration

SoC-MOBINET courseware[M-1] High-Level Synthesis19 Multicycle Operations  o i – operation  d i – delay for 1 ≤ j ≤ s, 1 ≤ k ≤ m for all o i  o k - d i

SoC-MOBINET courseware[M-1] High-Level Synthesis20 Multiple Operations per Cycle  New precedence relation  oi => oj -- oj is the nearest successor of oi for all o i => o k for all o i  o k 0

SoC-MOBINET courseware[M-1] High-Level Synthesis21 Pipelined Data Paths  l: fixed latency (integer multiple of a clock cycle)  | s i – s j |: integer multiple of l

SoC-MOBINET courseware[M-1] High-Level Synthesis22 Mutually Exclusive Operations  If o i, o j – two mutually exclusive operations,X(o i, o j ) = 1 otherwise X(o i, o j ) = 0  Both scheduled in control step k  Count function unit cost as 1, not 2  New 0/1 integer variable y k -- 0 if x i,k = x j,k = if otherwise  x i,k + x j,k = y k in constraint (2)

SoC-MOBINET courseware[M-1] High-Level Synthesis23 Variables’ Lifetime Consideration  Function unit cost for both schedules are the same, but fewer number of registers needed in Fig(a)

SoC-MOBINET courseware[M-1] High-Level Synthesis24 Variables’ Lifetime Consideration  SLK i,j – difference between the assigned control steps of o i, o j (o i  o j )  Minimize total step differences minimize

SoC-MOBINET courseware[M-1] High-Level Synthesis25 Experimental Results

SoC-MOBINET courseware[M-1] High-Level Synthesis26 Experimental Results  Fifth order wave filter  Containing 26 addition (1 cycle) & 8 multiplication (2 cycles) operations

SoC-MOBINET courseware[M-1] High-Level Synthesis27 Conclusion  Integer Linear Programming formulation (ILP)  minimize the function unit cost  Quite acceptable for practical synthesis  Always find the optimal solution  Different kinds of data path are taken into account

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