1. Local Memory optimizations
SEMINAR 3
Local Memory optimizations

2. Outline of the seminar Student presentations Local memory optimization
Results from last year
Basis for grading the works

3. Local memory bank conflicts
Local memory bank is 4 bytes wide and 256 bytes deep (AMD). 32 banks per CU
Bank conflicts are checked checked within a half-wavefront
Local memory performs best if there is one access to each bank by a half-wavefront or when the whole half-wavefront accesses the same bank (broadcast)
Bank conflict means that work items within a half-wavefront request values from same banks in a single request
Assuming a row work group (16,1,1) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

4. Explicit copy to local memory
__local uchar *local_left, __local uchar *local_right PASSED IN AS KERNEL ARGUMENTS const int2 gid = (int2)(get_global_id(0), get_global_id(1)); const int2 lid = (int2)(get_local_id(0), get_local_id(1)); // fill the left local memory buffer for (Ly = 0; Ly < local_height; Ly += get_local_size(1)) { for (Lx = 0; Lx < local_width; Lx += get_local_size(0)) { Lindex = (lid.y + Ly)*local_width + lid.x + Lx; Gindex = (gid.y + Ly) * width + gid.x + Lx; local_left[Lindex] = srcL[Gindex]; local_right[Lindex] = srcR[Gindex - MAX_DISP]; }

5. Results from 2016

6. Mali-T624 (Honor 6) results from 2016 OS Android 5.1.1
C (cpu, single thread) s OpenCL (gpu) s OpenCL Vectorization (gpu) s

7. Odroid instructions
Username and password for odroids are both ”odroid”
There is a Mali_SDK shortcut on the desktop
Open it and then open the samples folder
Copy the template folder and rename it
Copy your files to the folder and edit the Makefile
Replace the template.cpp with your .cpp files on the SOURCES line
On HEADERS line, include the required header files
On line EXECUTABLE, rename the executable if you wish
Open the MATE terminal
Go to the folder you created
Eg. cd /home/odroid/Desktop/Mali_OpenCL_SDK_v1.1.0/samples/your_folder
Build your project
Type ”make”
Run your project
./your_executable

8. Brief CodeXL instructions
1. In Visual Studio, open the CodeXL tap 2. Switch to profile mode 3. Choose the GPU: Performance Counters 4. Start CodeXL GPU Profiling

9. About the grading
If the work returned before the deadline at midnight
2. Everything works + final report and training diary returned
3. Minor optimizations (native functions, fast floating point math etc.)
4. Vector optimization
5. Local memory optimization
Extra +1 can be granted if CodeXL profiling performed and possible further actions to optimize the code based on the profiling feedback is given in the final report
CodeXL available in the workstations in TS135 and TS351
If e.g. Nvidia & Intel have similar tools they can be used as well