1. General Optimization Issues
Solving the exercise issues

2. To be tackled today Exercise 1 Exercise 2 Exercise 3 Exercise 4
Solving the loop problem SIZE = 128
Exercise 2
Solving the loop problem SIZE = 127
Exercise 3
Moving from SISD to SIMD mode, SIZE = 128
Exercise 4
Removing any expected stalls
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

3. Most optimized SIMD Floating point (32-bit)TigerSHARC instruction
xR3:0 = CB Q[j0 += 4]; yR3:0 = CB Q[k0 += 4]; xyFR4 = R5 * R6; xyFR7 = R8 + R9, FR10 = R8 - R9;;
xR3:0 = CB Q[j0 += 4]; /* Fetches 4 values on J BUS into x compute registers XR3, XR2, XR1, XR Increments J register and adjusts for circular buffer operation */
yR3:0 = CB Q[k0 += 4]; /* Fetches 4 values on J BUS into x compute registers XR3, XR2, XR1, XR Increments J register and adjusts for circular buffer operation */
xyFR4 = R5 * R6; /* Two multiplications XFR5 * XFR6 and YFR5 * YFR6 */
xyFR7 = R8 + R9, FR10 = R8 - R9;; /* Two additions XFR8 + XFR9 and YFR8 + YFR9 AND Two subtractions XFR8 - XFR9 and YFR8 - YFR9 */
/* Same register must be used either side of + and – operators */
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

4. Steps to optimize Get the algorithm to work in “C”
Determine how much time is available
If Timing already okay – quit
Determine maximum number of each type of operation (add, subtract, multiple, memory fetches)
Divide the calculated maximum by the number of available resources for that type of operation
The largest division result is the – in theory – number of cycles needed for the algorithm
If that minimum time is more than 100% of the time available – find a new algorithm
If that minimum time is less than 40% of the time available – perhaps you can optimize the code to meet the speed requirements
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

5. Code optimization – 32 bit integers or 32-bit floats
2 * SIZE additions
2 * SIZE Memory fetches
Left fetched on J-bus
And done in X-compute
Right fetched on K-bus
And done in Y-compute
SIZE / 2 cycles in theory
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

6. STAGE 1 Get the C++ code to work
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

7. Stage 2 – Rewrite in simplest format
Note naming convention
Single operation
per line
Note other changes
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

8. Step 3 -- Unwrap the loop Again Note naming convention
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

9. Step 4 Overlap the first and second parts of loops
Note
The “C++” code goes no
faster, but using this
format for translating into
parallel assembly code will
Step * N
Step 3 – 8 * (N / 2) + 2
Step 4 – 6 * (N / 2) + 2
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

10. Step 5A - Rearrange “start-up” and ending code
“Software” Pipeline
Move first read outside
Need to add “extra read” at the end of the loop
Timing 2 + (N/2 – 1) * 6
Need to adjust loop start
(Is it done correctly? Are we “one-out”)
CAUTION – NEED TO FIX
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

11. Step 5B - Rearrange “start-up” and ending code
Can now parallel additional
adds and memory fetches
Note loop still in error
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

12. Exercise 1 -- Get the loop control correct
BUFFER_SIZE = 1
BUFFER_SIZE = 2
BUFFER_SIZE = 4
BUFFER_SIZE = 5
BUFFER_SIZE = 8
BUFFER_SIZE = 128
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

13. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

14. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

15. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

16. Unrecognized second key error What is it? How do you fix it?
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

17. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

18. Exercise 2 -- Rewrite the code when it is known that BUFFER_SIZE = 129
But loop only handles 128
Since 129 / 2 = 128 / 2
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

19. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

20. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

21. Code to this point is SISD parallel optimization
SISD – single instruction single data
Using X_compute block and J memory bus
Next stage – SIMD – single instruction multiple data
Using X_compute block and J memory bus for left
Using Y_compute block and K memory bus for right
Will need similar but different code when you are doing FIR in Lab. 3
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

22. Exercise 3 -- BUFFER_SIZE = 128 Rewrite so that X and Y ops done together
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

23. 2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

24. Exercise 4 -- BUFFER_SIZE = 128 Rewrite so that expect no data dependency stalls
Leave this one for a while until we have handled multiple memory accesses as answer may changes
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada

25. Tackled today Exercise 1 Exercise 2 Exercise 3 Exercise 4
Solving the loop problem SIZE = 128
Exercise 2
Solving the loop problem SIZE = 127
Exercise 3
Moving from SISD to SIMD mode, SIZE = 128
Incomplete
Exercise 4
Removing any expected stalls – left for later
2/23/2019
Software Circular Buffer Issues, M. Smith, ECE, University of Calgary, Canada