$ gcc -O0 pagecount.c && ./a.out
0.01s to run 10000000 tests (0.64ns per test)
$ perf stat ./a.out
Performance counter stats for './a.out':
56.63 msec task-clock:u # 0.983 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
61 page-faults:u # 1.077 K/sec
215457754 cpu_core/cycles/u # 3.805 G/sec
<not counted> cpu_atom/cycles/u (0.00%)
1000134700 cpu_core/instructions/u # 17.662 G/sec
<not counted> cpu_atom/instructions/u (0.00%)
40029452 cpu_core/branches/u # 706.901 M/sec
<not counted> cpu_atom/branches/u (0.00%)
2466 cpu_core/branch-misses/u # 43.548 K/sec
<not counted> cpu_atom/branch-misses/u (0.00%)
1292746524 cpu_core/slots:u/ # 22.829 G/sec
1069684378 cpu_core/topdown-retiring/u # 82.7% Retiring
241871 cpu_core/topdown-bad-spec/u # 0.0% Bad Speculation
217992551 cpu_core/topdown-fe-bound/u # 16.9% Frontend Bound
5069594 cpu_core/topdown-be-bound/u # 0.4% Backend Bound
70974318 cpu_core/topdown-heavy-ops/u # 5.5% Heavy Operations # 77.2% Light Operations
241871 cpu_core/topdown-br-mispredict/u # 0.0% Branch Mispredict # 0.0% Machine Clears
50695942 cpu_core/topdown-fetch-lat/u # 3.9% Fetch Latency # 12.9% Fetch Bandwidth
80623 cpu_core/topdown-mem-bound/u # 0.0% Memory Bound # 0.4% Core Bound
0.057608809 seconds time elapsed
0.054232000 seconds user
0.003379000 seconds sys
$ gcc -O0 pagecount.c ; and ./a.out
0.01s to run 10000000 tests (0.73ns per test)
$ perf stat ./a.out
Performance counter stats for './a.out':
48.79 msec task-clock:u # 0.973 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
61 page-faults:u # 1.250 K/sec
189409587 cpu_core/cycles/u # 3.882 G/sec
<not counted> cpu_atom/cycles/u (0.00%)
1020134556 cpu_core/instructions/u # 20.907 G/sec
<not counted> cpu_atom/instructions/u (0.00%)
40029417 cpu_core/branches/u # 820.384 M/sec
<not counted> cpu_atom/branches/u (0.00%)
2482 cpu_core/branch-misses/u # 50.867 K/sec
<not counted> cpu_atom/branch-misses/u (0.00%)
1136457522 cpu_core/slots:u/ # 23.291 G/sec
1060693687 cpu_core/topdown-retiring/u # 93.3% Retiring
256805 cpu_core/topdown-bad-spec/u # 0.0% Bad Speculation
66850442 cpu_core/topdown-fe-bound/u # 5.9% Frontend Bound
8913392 cpu_core/topdown-be-bound/u # 0.8% Backend Bound
40110265 cpu_core/topdown-heavy-ops/u # 3.5% Heavy Operations # 89.8% Light Operations
256805 cpu_core/topdown-br-mispredict/u # 0.0% Branch Mispredict # 0.0% Machine Clears
8913392 cpu_core/topdown-fetch-lat/u # 0.8% Fetch Latency # 5.1% Fetch Bandwidth
0 cpu_core/topdown-mem-bound/u # 0.0% Memory Bound # 0.8% Core Bound
0.050146025 seconds time elapsed
0.046714000 seconds user
0.003306000 seconds sys
$ gcc -O2 pagecount.c ; and ./a.out
0.02s to run 10000000 tests (1.64ns per test)
$ perf stat ./a.out
Performance counter stats for './a.out':
32.84 msec task-clock:u # 0.949 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
61 page-faults:u # 1.857 K/sec
127796253 cpu_core/cycles/u # 3.891 G/sec
<not counted> cpu_atom/cycles/u (0.00%)
320134368 cpu_core/instructions/u # 9.747 G/sec
<not counted> cpu_atom/instructions/u (0.00%)
20029370 cpu_core/branches/u # 609.824 M/sec
<not counted> cpu_atom/branches/u (0.00%)
2388 cpu_core/branch-misses/u # 72.706 K/sec
<not counted> cpu_atom/branch-misses/u (0.00%)
766777518 cpu_core/slots:u/ # 23.346 G/sec
339787684 cpu_core/topdown-retiring/u # 44.5% Retiring
9555 cpu_core/topdown-bad-spec/u # 0.0% Bad Speculation
51118501 cpu_core/topdown-fe-bound/u # 6.7% Frontend Bound
372864361 cpu_core/topdown-be-bound/u # 48.8% Backend Bound
39090618 cpu_core/topdown-heavy-ops/u # 5.1% Heavy Operations # 39.4% Light Operations
8600 cpu_core/topdown-br-mispredict/u # 0.0% Branch Mispredict # 0.0% Machine Clears
20306 cpu_core/topdown-fetch-lat/u # 0.0% Fetch Latency # 6.7% Fetch Bandwidth
87202149 cpu_core/topdown-mem-bound/u # 11.4% Memory Bound # 37.4% Core Bound
0.034608481 seconds time elapsed
0.031066000 seconds user
0.003415000 seconds sys
$ gcc -O2 pagecount.c ; and ./a.out
0.00s to run 10000000 tests (0.06ns per test)
$ perf stat ./a.out
Performance counter stats for './a.out':
17.92 msec task-clock:u # 0.972 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
61 page-faults:u # 3.404 K/sec
61513373 cpu_core/cycles/u # 3.432 G/sec
<not counted> cpu_atom/cycles/u (0.00%)
310134668 cpu_core/instructions/u # 17.305 G/sec
<not counted> cpu_atom/instructions/u (0.00%)
20029441 cpu_core/branches/u # 1.118 G/sec
<not counted> cpu_atom/branches/u (0.00%)
2444 cpu_core/branch-misses/u # 136.371 K/sec
<not counted> cpu_atom/branch-misses/u (0.00%)
369052428 cpu_core/slots:u/ # 20.592 G/sec
299583735 cpu_core/topdown-retiring/u # 81.2% Retiring
0 cpu_core/topdown-bad-spec/u # 0.0% Bad Speculation
4341793 cpu_core/topdown-fe-bound/u # 1.2% Frontend Bound
65126899 cpu_core/topdown-be-bound/u # 17.6% Backend Bound
10130850 cpu_core/topdown-heavy-ops/u # 2.7% Heavy Operations # 78.4% Light Operations
0 cpu_core/topdown-br-mispredict/u # 0.0% Branch Mispredict # 0.0% Machine Clears
1447264 cpu_core/topdown-fetch-lat/u # 0.4% Fetch Latency # 0.8% Fetch Bandwidth
0 cpu_core/topdown-mem-bound/u # 0.0% Memory Bound # 17.6% Core Bound
0.018436405 seconds time elapsed
0.018435000 seconds user
0.000000000 seconds sys
The measuraments using the time.h API show performance improvements with the optimizations, but using perf stat gave worse data compared to the ones registered in solution/dotproduct.c comments, the fully optimized version had worse Retiring, Backend Bound and Memory Bound than the least optimized version. Removing the get_vec_element call was one of the best optimizations. I've created a bench.c to remove the testing framework and only run dotproduct stuff.
Using the least optimized dotproduct implementation:
$ gcc -O2 bench.c vec.c dotproduct.c
$ perf stat ./a.out
0.16s to take product of length 100000000 vectors (1.55 ns per element)
Performance counter stats for './a.out':
441.38 msec task-clock:u # 0.998 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
1817 page-faults:u # 4.117 K/sec
1236123531 cpu_core/cycles/u # 2.801 G/sec
<not counted> cpu_atom/cycles/u (0.00%)
6800140661 cpu_core/instructions/u # 15.407 G/sec
<not counted> cpu_atom/instructions/u (0.00%)
2000032178 cpu_core/branches/u # 4.531 G/sec
<not counted> cpu_atom/branches/u (0.00%)
10791 cpu_core/branch-misses/u # 24.448 K/sec
<not counted> cpu_atom/branch-misses/u (0.00%)
7414936686 cpu_core/slots:u/ # 16.799 G/sec
6280887545 cpu_core/topdown-retiring/u # 85.0% Retiring
0 cpu_core/topdown-bad-spec/u # 0.0% Bad Speculation
0 cpu_core/topdown-fe-bound/u # 0.0% Frontend Bound
1104970957 cpu_core/topdown-be-bound/u # 15.0% Backend Bound
494329112 cpu_core/topdown-heavy-ops/u # 6.7% Heavy Operations # 78.3% Light Operations
0 cpu_core/topdown-br-mispredict/u # 0.0% Branch Mispredict # 0.0% Machine Clears
0 cpu_core/topdown-fetch-lat/u # 0.0% Fetch Latency # 0.0% Fetch Bandwidth
1046814590 cpu_core/topdown-mem-bound/u # 14.2% Memory Bound # 0.8% Core Bound
0.442298907 seconds time elapsed
0.262436000 seconds user
0.179373000 seconds sys
Using the most optimized dotproduct implementation:
$ gcc -O2 bench.c vec.c dotproduct.c
$ perf stat ./a.out
0.06s to take product of length 100000000 vectors (0.56 ns per element)
Performance counter stats for './a.out':
403.53 msec task-clock:u # 0.997 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
1816 page-faults:u # 4.500 K/sec
1100559201 cpu_core/cycles/u # 2.727 G/sec
<not counted> cpu_atom/cycles/u (0.00%)
3400140631 cpu_core/instructions/u # 8.426 G/sec
<not counted> cpu_atom/instructions/u (0.00%)
925032129 cpu_core/branches/u # 2.292 G/sec
<not counted> cpu_atom/branches/u (0.00%)
9070 cpu_core/branch-misses/u # 22.476 K/sec
<not counted> cpu_atom/branch-misses/u (0.00%)
6601863078 cpu_core/slots:u/ # 16.360 G/sec
3080869436 cpu_core/topdown-retiring/u # 46.7% Retiring
1052841 cpu_core/topdown-bad-spec/u # 0.0% Bad Speculation
25889659 cpu_core/topdown-fe-bound/u # 0.4% Frontend Bound
3495103982 cpu_core/topdown-be-bound/u # 52.9% Backend Bound
207117273 cpu_core/topdown-heavy-ops/u # 3.1% Heavy Operations # 43.5% Light Operations
526420 cpu_core/topdown-br-mispredict/u # 0.0% Branch Mispredict # 0.0% Machine Clears
1579262 cpu_core/topdown-fetch-lat/u # 0.0% Fetch Latency # 0.4% Fetch Bandwidth
2977310799 cpu_core/topdown-mem-bound/u # 45.1% Memory Bound # 7.8% Core Bound
0.404560238 seconds time elapsed
0.257149000 seconds user
0.146887000 seconds sys