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tracing: Only calculate stats of tracepoint benchmarks for 2^32 times 

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 <rostedt@goodmis.org>
hifive-unleashed-5.1
Steven Rostedt (Red Hat) 2014-06-05 23:34:02 -04:00 committed by Steven Rostedt
parent 72e2fe38ea
commit 34839f5a69
1 changed files with 30 additions and 7 deletions
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37
kernel/trace/trace_benchmark.c
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@ -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;
}