PC Lab 5

Session 5

Task: run an open-source profiler (valgrind & gprof or visual studio) and improve performance of keypoint extraction in ASIFT C++ code

1. Download ASIFT project from here: http://www.ipol.im/pub/art/2011/my-asift/

2. Run demo_ASIFT with the two included Adams as input images from the Sixtine Chapel. Horizontal result should look like this:

3. Modify code to only do "compute_asift_keypoints" (matching is not interesting, since it was covered in the previous session)

4. Run the valgrind profiler

eg, for dummy program:

g++ -std=c++11 dummy.cpp -o dummy (compile program dummy)

valgrind --tool=callgrind ./dummy (run the program with callgrind; generates a file callgrind.out.12345 that can be viewed with kcachegrind)

kcachegrind whateverprofile.callgrind // open profile.callgrind with kcachegrind

5. Look over the report, and propose 3 leaf-functions (functions that do not call other functions) for offloading towards a coprocessor. Write the reason for choosing each of them, and how much time is gained by offloading them. Assume coprocessor works at infinite clock, but data is transferred at 200 MB/s. Hint: Use the callgraph (by installing the graphiviz package). Keep a snapshot with the analysis report as proof. Send results/comments/snapshot(s) by e-mail to the teacher.

Note: Valgrind is also great for checking memory leaks:

valgrind --leak-check=full <path>

valgrind --tool=memcheck <path>

Points (out of 10) vs. expected performance:

10 points for identifying 3 most-heavy leaf-functions and correct (within 10%) computation for offloading impact. DESCRIBE_INSTR.

9 points for identifying 3 most-heavy leaf-functions and acceptable (within 20%) computation for offloading impact. DESCRIBE_INSTR.

8 points for identifying 2 most-heavy leaf-functions and correct (within 10%) computation for offloading impact. DESCRIBE_INSTR.

7 points for identifying 2 most-heavy leaf-functions and resonable (within 30%) computation for offloading impact. DESCRIBE_INSTR.

6 points for identifying 1 most-heavy leaf-functions and resonable (within 30%) computation for offloading impact. DESCRIBE_INSTR.

5 points for identifying 1 most-heavy leaf-functions and coarse (within 50%) computation for offloading impact. DESCRIBE_INSTR.

DESCRIBE_INSTR = Write as function prototype with result, name, operand number, types and size (similar to Intel Intrinsics Guide). Write a natural-language description of the behaviour (or alternative-le, the formal description as in Intel Intrinsics Guide)