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Fix public issue #38: Make the microbenchmark framework handle 

properly cases where gettimeofday() can stand return the same
result twice (as sometimes on GNU/Hurd) or go backwards
(as when the user adjusts the clock). We avoid a division-by-zero,
and put a lower bound on the number of iterations -- the same
amount as we use to calibrate.

We should probably use CLOCK_MONOTONIC for platforms that support
it, to be robust against clock adjustments; we already use Windows'
monotonic timers. However, that's for a later changelist.

R=csilvers
DELTA=7  (5 added, 0 deleted, 2 changed)


Revision created by MOE tool push_codebase.
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git-svn-id: https://snappy.googlecode.com/svn/trunk@34 03e5f5b5-db94-4691-08a0-1a8bf15f6143
This commit is contained in:
snappy.mirrorbot@gmail.com 2011-05-09 21:28:45 +00:00
parent d8d481427a
commit f7b105683c
1 changed files with 7 additions and 2 deletions
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9
snappy-test.cc
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@ -182,11 +182,16 @@ void Benchmark::Run() {
(*function_)(kCalibrateIterations, test_case_num);
StopBenchmarkTiming();
// Let each test case run for about 200ms.
// Let each test case run for about 200ms, but at least as many
// as we used to calibrate.
// Run five times and pick the median.
const int kNumRuns = 5;
const int kMedianPos = kNumRuns / 2;
int num_iterations = 200000 * kCalibrateIterations / benchmark_real_time_us;
int num_iterations = 0;
if (benchmark_real_time_us > 0) {
num_iterations = 200000 * kCalibrateIterations / benchmark_real_time_us;
}
num_iterations = max(num_iterations, kCalibrateIterations);
BenchmarkRun benchmark_runs[kNumRuns];
for (int run = 0; run < kNumRuns; ++run) {