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Remove countMaskInv caching in bench framework

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We were saving a div by caching the inverse as a float, but this
ended up requiring a int -> float -> int conversion, which takes
almost as much time as the difference between float mul and div.

There are lots of other more pressing issues with the bench
framework which probably require simply removing the adaptive
iteration count stuff anyway.
This commit is contained in:
Matt Corallo
2017-09-11 15:24:45 -04:00
parent 31e72b284e
commit 0b1b9148cd
2 changed files with 3 additions and 6 deletions
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6
src/bench/bench.cpp
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@@ -55,13 +55,13 @@ bool benchmark::State::KeepRunning()
else {
now = gettimedouble();
double elapsed = now - lastTime;
double elapsedOne = elapsed * countMaskInv;
double elapsedOne = elapsed / (countMask + 1);
if (elapsedOne < minTime) minTime = elapsedOne;
if (elapsedOne > maxTime) maxTime = elapsedOne;
// We only use relative values, so don't have to handle 64-bit wrap-around specially
nowCycles = perf_cpucycles();
uint64_t elapsedOneCycles = (nowCycles - lastCycles) * countMaskInv;
uint64_t elapsedOneCycles = (nowCycles - lastCycles) / (countMask + 1);
if (elapsedOneCycles < minCycles) minCycles = elapsedOneCycles;
if (elapsedOneCycles > maxCycles) maxCycles = elapsedOneCycles;
@@ -69,7 +69,6 @@ bool benchmark::State::KeepRunning()
// If the execution was much too fast (1/128th of maxElapsed), increase the count mask by 8x and restart timing.
// The restart avoids including the overhead of this code in the measurement.
countMask = ((countMask<<3)|7) & ((1LL<<60)-1);
countMaskInv = 1./(countMask+1);
count = 0;
minTime = std::numeric_limits<double>::max();
maxTime = std::numeric_limits<double>::min();
@@ -81,7 +80,6 @@ bool benchmark::State::KeepRunning()
uint64_t newCountMask = ((countMask<<1)|1) & ((1LL<<60)-1);
if ((count & newCountMask)==0) {
countMask = newCountMask;
countMaskInv = 1./(countMask+1);
}
}
}