Re: SMS scheduling

[Canqun Yang <canqun at nudt dot edu dot cn>]

Mostafa Hagog <MUSTAFA@il.ibm.com>:

> 
> Canqun Yang <canqun@nudt.edu.cn> wrote on 28/09/2004 
11:06:29:
>
> > Hi, all
> >
> > I tested the Swing Modulo Scheduling of GCC. For
> > simple program, the numerical caculation of PI, it
> > achieves significant speedup on IA64. But, for 
little
> > bit complex programs, the SMS can hardly work out a
> > successful schedule.
> >
> > The algorithms implemented by Ayal and Mostafa are
> > correct. It seems that the SMS itself is wrong. The
> > schedule priority order calculated by SMS is much
> > different from normal MinDist algorithm.
>
> SMS prioritizes the nodes using critical patch based
> heuristic - the main idea is that instructions that 
are
> on the critical path are less flexible in means of
> scheduling.
> Why do you think that the priority order should be
> according to MinDist algorithm (what is the minimum
> distance in this case)? Can you provide an example
> that supports this?
>
> > Besides this,
> > SMS is not sensitive to II. Is SMS really wrong?
>
> The node ordering step in SMS is not sensitive to II
> (as mentioned before it is based on critical path
> heuristic).  However, the scheduling step is 
sensitive
> to II - failing to schedule the nodes of a loop 
within
> II cycles will lead to try scheduling the nodes again
> within II + 1 cycles.
>
>
> Mostafa.
>

An example for SMS.

Content

  1. Fortran source
     'doloop_get_register' was modified to let it 
return the needed value.

  2. vcg file of data dependence graph

  3. node order parameters

  4. node order calculated by SMS

  5. failed schedule
     The schedule will block on nearly the same insn 
node while the II is increasing.

  6. node order calculated by mindist algorithm
     mindist is an algorithm for computing the minmum 
permissible time interval between every pair of 
operations. It is a time consuming algorithm.
     Ref. Iterative Modulo Scheduling, B. Ramakrisha 
Rau, Compiler and Architecture Research, HPL-94-115, 
1995.

  7. successful schedule


1. Fortran source

#define N 32767
double uold[N], vold[N], alpha;

void calc3 ()
{
  int i;

  for (i = 0; i < N; i++)
    {
      uold[i] += alpha;
      vold[i] += alpha;
    }
}


2. vcg file of data dependence graph

graph: {
node: {title: "0_29" info1: "(insn 29 23 30 1 (set 
(reg:DF 355)
        (mem/s:DF (reg/f:DI 351 [ ivtmp.19 ]) [3 uold 
S8 A64])) 25 {*movdf_internal} (nil)
    (nil))
"}
edge: { sourcename: "0_29" targetname: "2_31" 
label: "0_0"}
edge: { sourcename: "0_29" targetname: "1_30" 
label: "6_0"}
node: {title: "1_30" info1: "(insn 30 29 31 1 (set 
(reg:DF 356)
        (plus:DF (reg:DF 355)
            (reg:DF 353 [ alpha.1 ]))) 133 {adddf3} 
(insn_list:REG_DEP_TRUE 29 (nil))
    (expr_list:REG_DEAD (reg:DF 355)
        (nil)))
"}
edge: { sourcename: "1_30" targetname: "2_31" 
label: "7_0"}
node: {title: "2_31" info1: "(insn 31 30 35 1 (set 
(mem/s:DF (post_inc:DI (reg/f:DI 351 [ 

ivtmp.19 ])) [3 uold S8 A64])
        (reg:DF 356)) 25 {*movdf_internal} 
(insn_list:REG_DEP_TRUE 30 

(insn_list:REG_DEP_ANTI 29 (nil)))
    (expr_list:REG_DEAD (reg:DF 356)
        (expr_list:REG_INC (reg/f:DI 351 [ ivtmp.19 ])
            (nil))))
"}
backedge: {color: red sourcename: "2_31" 
targetname: "2_31" label: "1_1"}
backedge: {color: red sourcename: "2_31" 
targetname: "0_29" label: "1_1"}
edge: { sourcename: "2_31" targetname: "6_71" 
label: "0_0"}
backedge: {color: red sourcename: "2_31" 
targetname: "3_35" label: "1_1"}
backedge: {color: red sourcename: "2_31" 
targetname: "0_29" label: "1_1"}
node: {title: "3_35" info1: "(insn 35 31 36 1 (set 
(reg:DF 357)
        (mem/s:DF (reg/f:DI 350 [ ivtmp.23 ]) [3 vold 
S8 A64])) 25 {*movdf_internal} (nil)
    (nil))
"}
edge: { sourcename: "3_35" targetname: "5_37" 
label: "0_0"}
edge: { sourcename: "3_35" targetname: "4_36" 
label: "6_0"}
backedge: {color: red sourcename: "3_35" 
targetname: "2_31" label: "0_1"}
node: {title: "4_36" info1: "(insn 36 35 37 1 (set 
(reg:DF 358)
        (plus:DF (reg:DF 353 [ alpha.1 ])
            (reg:DF 357))) 133 {adddf3} 
(insn_list:REG_DEP_TRUE 35 (nil))
    (expr_list:REG_DEAD (reg:DF 357)
        (nil)))
"}
edge: { sourcename: "4_36" targetname: "5_37" 
label: "7_0"}
node: {title: "5_37" info1: "(insn 37 36 39 1 (set 
(mem/s:DF (post_inc:DI (reg/f:DI 350 [ 

ivtmp.23 ])) [3 vold S8 A64])
        (reg:DF 358)) 25 {*movdf_internal} 
(insn_list:REG_DEP_TRUE 36 

(insn_list:REG_DEP_ANTI 35 (nil)))
    (expr_list:REG_DEAD (reg:DF 358)
        (expr_list:REG_INC (reg/f:DI 350 [ ivtmp.23 ])
            (nil))))
"}
backedge: {color: red sourcename: "5_37" 
targetname: "5_37" label: "1_1"}
backedge: {color: red sourcename: "5_37" 
targetname: "3_35" label: "1_1"}
edge: { sourcename: "5_37" targetname: "6_71" 
label: "0_0"}
backedge: {color: red sourcename: "5_37" 
targetname: "3_35" label: "1_1"}
backedge: {color: red sourcename: "5_37" 
targetname: "2_31" label: "0_1"}
backedge: {color: red sourcename: "5_37" 
targetname: "0_29" label: "1_1"}
node: {title: "6_71" info1: "(jump_insn 71 40 81 1 
(parallel [
            (set (pc)
                (if_then_else (ne (reg:DI 332 ar.lc)
                        (const_int 0 [0x0]))
                    (label_ref 22)
                    (pc)))
            (set (reg:DI 332 ar.lc)
                (if_then_else:DI (ne (reg:DI 332 ar.lc)
                        (const_int 0 [0x0]))
                    (plus:DI (reg:DI 332 ar.lc)
                        (const_int -1 
[0xffffffffffffffff]))
                    (reg:DI 332 ar.lc)))
        ]) 223 {doloop_end_internal} 
(insn_list:REG_DEP_OUTPUT 31 (insn_list:REG_DEP_OUTPUT 

37 (nil)))
    (nil))
"}
}


3. node order parameters

#   ASAP   ALAP  HEIGHT MOB  DEPTH
0    0      0     13     0     0
1    6      6     7      0     6
2    13     13    0      0     13
3    0      0     13     0     0
4    6      6     7      0     6
5    13     13    0      0     13
6    13     13    0      0     13



4. node order calculated by SMS
  2, 5, 1, 4, 0, 3, 6


5. failed schedule

;; Function calc3

SMS single-bb-loop
SMS doloop
SMS built-ddg 7
SMS num-loads 2
SMS num-stores 2
SMS const-doloop 32766
SMS iis 14 14 28 (rec_mii, mii, maxii)
Starting with ii=14
Trying to schedule node 2 in (13 .. 27) step 1
Schedule in 13
Trying to schedule node 5 in (27 .. 13) step -1
Schedule in 27
Trying to schedule node 1 in (6 .. -8) step -1
Schedule in 6
Trying to schedule node 4 in (20 .. 6) step -1
Schedule in 20
Trying to schedule node 0 in (14 .. 1) step 1
Starting with ii=15
Trying to schedule node 2 in (13 .. 28) step 1
Schedule in 13
Trying to schedule node 5 in (28 .. 13) step -1
Schedule in 28
Trying to schedule node 1 in (6 .. -9) step -1
Schedule in 6
Trying to schedule node 4 in (21 .. 6) step -1
Schedule in 21
Trying to schedule node 0 in (14 .. 1) step 1
Starting with ii=16
Trying to schedule node 2 in (13 .. 29) step 1
Schedule in 13
Trying to schedule node 5 in (29 .. 13) step -1
Schedule in 29
Trying to schedule node 1 in (6 .. -10) step -1
Schedule in 6
Trying to schedule node 4 in (22 .. 6) step -1
Schedule in 22
Trying to schedule node 0 in (14 .. 1) step 1
Starting with ii=17
Trying to schedule node 2 in (13 .. 30) step 1
Schedule in 13
Trying to schedule node 5 in (30 .. 13) step -1
Schedule in 30
Trying to schedule node 1 in (6 .. -11) step -1
Schedule in 6
Trying to schedule node 4 in (23 .. 6) step -1
Schedule in 23
Trying to schedule node 0 in (14 .. 1) step 1
Starting with ii=18
......


6. node order calculated by mindist algorithm
  3, 1, 4, 0, 2, 5, 6


7. The successful schedule.

;; Function calc3

SMS single-bb-loop
SMS doloop
SMS built-ddg 7
SMS num-loads 2
SMS num-stores 2
SMS const-doloop 32766
SMS iis 14 14 28 (rec_mii, mii, maxii)
Starting with ii=14
Trying to schedule node 3 in (0 .. 14) step 1
Schedule in 0
Trying to schedule node 1 in (6 .. 20) step 1
Schedule in 6
Trying to schedule node 4 in (6 .. 20) step 1
Schedule in 6
Trying to schedule node 0 in (0 .. -14) step -1
Schedule in 0
Trying to schedule node 2 in (13 .. 13) step 1
Starting with ii=15
Trying to schedule node 3 in (0 .. 15) step 1
Schedule in 0
Trying to schedule node 1 in (6 .. 21) step 1
Schedule in 6
Trying to schedule node 4 in (6 .. 21) step 1
Schedule in 6
Trying to schedule node 0 in (0 .. -15) step -1
Schedule in 0
Trying to schedule node 2 in (13 .. 14) step 1
Schedule in 13
Trying to schedule node 5 in (13 .. 14) step 1
Schedule in 13
SMS succeeded 15 1 (with ii, sc)

 



Canqun Yang
Creative Compiler Research Group.
National University of Defense Technology, China.