Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 34839f5a authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
Browse files

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: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 72e2fe38

kernel/trace/trace_benchmark.c

+30 −7
Original line number Diff line number Diff line
@@ -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;

}