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slightly increase tolerance to clock speed variation

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This commit is contained in:
Benoit Jacob 2015-03-05 14:41:16 -05:00
parent 5db2baa573
commit 4ab01f7c21
1 changed files with 13 additions and 11 deletions
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24
bench/benchmark-blocking-sizes.cpp
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@ -369,12 +369,14 @@ void try_run_some_benchmarks(
// Ensure that clock speed is as expected // Ensure that clock speed is as expected
float current_clock_speed = measure_clock_speed(); float current_clock_speed = measure_clock_speed();
// we only allow 1% higher clock speeds, because we want to know the // The tolerance needs to be smaller than the relative difference between
// clock speed with good accuracy, and this should only cause restarts // clock speeds that a device could operate under.
// at the beginning of the benchmarks run. // It seems unlikely that a device would be throttling clock speeds by
const float tolerance_higher_clock_speed = 1.01f; // amounts smaller than 2%.
// With a value of 1%, I was getting within noise on a Sandy Bridge.
const float clock_speed_tolerance = 0.02f;
if (current_clock_speed > tolerance_higher_clock_speed * max_clock_speed) { if (current_clock_speed > (1 + clock_speed_tolerance) * max_clock_speed) {
// Clock speed is now higher than we previously measured. // Clock speed is now higher than we previously measured.
// Either our initial measurement was inaccurate, which won't happen // Either our initial measurement was inaccurate, which won't happen
// too many times as we are keeping the best clock speed value and // too many times as we are keeping the best clock speed value and
@ -390,12 +392,9 @@ void try_run_some_benchmarks(
return; return;
} }
// we are a bit more tolerant to lower clock speeds because we don't want
// to cause sleeps and reruns all the time.
const float tolerance_lower_clock_speed = 0.98f;
bool rerun_last_tests = false; bool rerun_last_tests = false;
if (current_clock_speed < tolerance_lower_clock_speed * max_clock_speed) { if (current_clock_speed < (1 - clock_speed_tolerance) * max_clock_speed) {
cerr << "Measurements completed so far: " cerr << "Measurements completed so far: "
<< 100.0f * ratio_done << 100.0f * ratio_done
<< " % " << endl; << " % " << endl;
@ -405,7 +404,7 @@ void try_run_some_benchmarks(
unsigned int seconds_to_sleep_if_lower_clock_speed = 1; unsigned int seconds_to_sleep_if_lower_clock_speed = 1;
while (current_clock_speed < tolerance_lower_clock_speed * max_clock_speed) { while (current_clock_speed < (1 - clock_speed_tolerance) * max_clock_speed) {
if (seconds_to_sleep_if_lower_clock_speed > 300) { if (seconds_to_sleep_if_lower_clock_speed > 300) {
cerr << "Sleeping longer probably won't make a difference. Giving up." << endl; cerr << "Sleeping longer probably won't make a difference. Giving up." << endl;
cerr << "Things to try:" << endl; cerr << "Things to try:" << endl;
@ -479,9 +478,12 @@ void run_benchmarks(vector<benchmark_t>& benchmarks)
max_clock_speed = max(max_clock_speed, measure_clock_speed()); max_clock_speed = max(max_clock_speed, measure_clock_speed());
} }
double time_start = timer.getRealTime(); double time_start = 0.0;
size_t first_benchmark_to_run = 0; size_t first_benchmark_to_run = 0;
while (first_benchmark_to_run < benchmarks.size()) { while (first_benchmark_to_run < benchmarks.size()) {
if (first_benchmark_to_run == 0) {
time_start = timer.getRealTime();
}
try_run_some_benchmarks(benchmarks, try_run_some_benchmarks(benchmarks,
time_start, time_start,
first_benchmark_to_run, first_benchmark_to_run,