From: "Steven Rostedt (Red Hat)" <[email protected]> When calculating the average and standard deviation, it is required that the count be less than UINT_MAX, otherwise the do_div() will get undefined results. After 2^32 counts of data, the average and standard deviation should pretty much be set anyway.
Signed-off-by: Steven Rostedt <[email protected]> --- kernel/trace/trace_benchmark.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c index 8bd3365a65b2..40a14cbcf8e0 100644 --- a/kernel/trace/trace_benchmark.c +++ b/kernel/trace/trace_benchmark.c @@ -16,7 +16,10 @@ static u64 bm_last; static u64 bm_max; static u64 bm_min; static u64 bm_first; -static s64 bm_cnt; +static u64 bm_cnt; +static u64 bm_stddev; +static unsigned int bm_avg; +static unsigned int bm_std; /* * This gets called in a loop recording the time it took to write @@ -66,22 +69,35 @@ static void trace_do_benchmark(void) bm_last = delta; - bm_total += delta; - bm_totalsq += delta * delta; - if (delta > bm_max) bm_max = delta; if (!bm_min || delta < bm_min) bm_min = delta; + /* + * When bm_cnt is greater than UINT_MAX, it breaks the statistics + * accounting. Freeze the statistics when that happens. + * We should have enough data for the avg and stddev anyway. + */ + if (bm_cnt > UINT_MAX) { + scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, + "last=%llu first=%llu max=%llu min=%llu ** avg=%u std=%d std^2=%lld", + bm_last, bm_first, bm_max, bm_min, bm_avg, bm_std, bm_stddev); + return; + } + + bm_total += delta; + bm_totalsq += delta * delta; + + if (bm_cnt > 1) { /* * Apply Welford's method to calculate standard deviation: * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) */ stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total; - do_div(stddev, bm_cnt); - do_div(stddev, bm_cnt - 1); + do_div(stddev, (u32)bm_cnt); + do_div(stddev, (u32)bm_cnt - 1); } else stddev = 0; @@ -119,6 +135,10 @@ static void trace_do_benchmark(void) scnprintf(bm_str, BENCHMARK_EVENT_STRLEN, "last=%llu first=%llu max=%llu min=%llu avg=%u std=%d std^2=%lld", bm_last, bm_first, bm_max, bm_min, avg, std, stddev); + + bm_std = std; + bm_avg = avg; + bm_stddev = stddev; } static int benchmark_event_kthread(void *arg) @@ -170,6 +190,9 @@ void trace_benchmark_unreg(void) bm_max = 0; bm_min = 0; bm_cnt = 0; - /* bm_first doesn't need to be reset but reset it anyway */ + /* These don't need to be reset but reset them anyway */ bm_first = 0; + bm_std = 0; + bm_avg = 0; + bm_stddev = 0; } -- 2.0.0.rc2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
