Commit 4a75e8c3 authored by Gabriele Monaco's avatar Gabriele Monaco Committed by Namhyung Kim
Browse files

perf ftrace latency: variable histogram buckets 



The max-latency value can make the histogram smaller, but not larger, we
have a maximum of 22 buckets and specifying a max-latency that would
require more buckets has no effect.

Dynamically allocate the buckets and compute the bucket number from the
max latency as (max-min) / range + 2

If the maximum is not specified, we still set the bucket number to 22
and compute the maximum accordingly.

Fail if the maximum is smaller than min+range, this way we make sure we
always have 3 buckets: those below min, those above max and one in the
middle.

Since max-latency is not available in log2 mode, always use 22 buckets.

Signed-off-by: default avatarGabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/r/20250207080446.77630-1-gmonaco@redhat.com


Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent f4dc5a33

tools/perf/builtin-ftrace.c

+41 −16
Original line number Diff line number Diff line
@@ -733,6 +733,7 @@ static void make_histogram(struct perf_ftrace *ftrace, int buckets[], 
{

	int min_latency = ftrace->min_latency;

	int max_latency = ftrace->max_latency;

	unsigned int bucket_num = ftrace->bucket_num;

	char *p, *q;

	char *unit;

	double num;
@@ -797,10 +798,10 @@ static void make_histogram(struct perf_ftrace *ftrace, int buckets[], 
			if (num > 0) // 1st entry: [ 1 unit .. bucket_range units ]

				i = num / ftrace->bucket_range + 1;

			if (num >= max_latency - min_latency)

				i = NUM_BUCKET -1;

				i = bucket_num -1;

		}

		if (i >= NUM_BUCKET)

			i = NUM_BUCKET - 1;

		if ((unsigned)i >= bucket_num)

			i = bucket_num - 1;



		num += min_latency;

do_inc:
@@ -820,13 +821,14 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
{

	int min_latency = ftrace->min_latency;

	bool use_nsec = ftrace->use_nsec;

	int i;

	unsigned int bucket_num = ftrace->bucket_num;

	unsigned int i;

	int total = 0;

	int bar_total = 46;  /* to fit in 80 column */

	char bar[] = "###############################################";

	int bar_len;



	for (i = 0; i < NUM_BUCKET; i++)

	for (i = 0; i < bucket_num; i++)

		total += buckets[i];



	if (total == 0) {
@@ -843,7 +845,7 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
	       0, min_latency ?: 1, use_nsec ? "ns" : "us",

	       buckets[0], bar_len, bar, bar_total - bar_len, "");



	for (i = 1; i < NUM_BUCKET - 1; i++) {

	for (i = 1; i < bucket_num - 1; i++) {

		unsigned int start, stop;

		const char *unit = use_nsec ? "ns" : "us";
@@ -881,11 +883,11 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
		       bar_total - bar_len, "");

	}



	bar_len = buckets[NUM_BUCKET - 1] * bar_total / total;

	bar_len = buckets[bucket_num - 1] * bar_total / total;

	if (!ftrace->bucket_range) {

		printf("  %4d - %-4s %s", 1, "...", use_nsec ? "ms" : "s ");

	} else {

		unsigned int upper_outlier = (NUM_BUCKET - 2) * ftrace->bucket_range + min_latency;

		unsigned int upper_outlier = (bucket_num - 2) * ftrace->bucket_range + min_latency;

		if (upper_outlier > ftrace->max_latency)

			upper_outlier = ftrace->max_latency;
@@ -897,7 +899,7 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
			printf("  %4d - %4s %s", upper_outlier, "...", use_nsec ? "ns" : "us");

		}

	}

	printf(" | %10d | %.*s%*s |\n", buckets[NUM_BUCKET - 1],

	printf(" | %10d | %.*s%*s |\n", buckets[bucket_num - 1],

	       bar_len, bar, bar_total - bar_len, "");



	printf("\n# statistics  (in %s)\n", ftrace->use_nsec ? "nsec" : "usec");
@@ -997,7 +999,7 @@ static int __cmd_latency(struct perf_ftrace *ftrace) 
	struct pollfd pollfd = {

		.events = POLLIN,

	};

	int buckets[NUM_BUCKET] = { };

	int *buckets;



	trace_fd = prepare_func_latency(ftrace);

	if (trace_fd < 0)
@@ -1011,6 +1013,12 @@ static int __cmd_latency(struct perf_ftrace *ftrace) 


	evlist__start_workload(ftrace->evlist);



	buckets = calloc(ftrace->bucket_num, sizeof(*buckets));

	if (buckets == NULL) {

		pr_err("failed to allocate memory for the buckets\n");

		goto out;

	}



	line[0] = '\0';

	while (!done) {

		if (poll(&pollfd, 1, -1) < 0)
@@ -1030,7 +1038,7 @@ static int __cmd_latency(struct perf_ftrace *ftrace) 
	if (workload_exec_errno) {

		const char *emsg = str_error_r(workload_exec_errno, buf, sizeof(buf));

		pr_err("workload failed: %s\n", emsg);

		goto out;

		goto out_free_buckets;

	}



	/* read remaining buffer contents */
@@ -1045,6 +1053,8 @@ static int __cmd_latency(struct perf_ftrace *ftrace) 


	display_histogram(ftrace, buckets);



out_free_buckets:

	free(buckets);

out:

	close(trace_fd);

	cleanup_func_latency(ftrace);
@@ -1634,7 +1644,7 @@ int cmd_ftrace(int argc, const char **argv) 
	OPT_UINTEGER(0, "min-latency", &ftrace.min_latency,

		    "Minimum latency (1st bucket). Works only with --bucket-range."),

	OPT_UINTEGER(0, "max-latency", &ftrace.max_latency,

		    "Maximum latency (last bucket). Works only with --bucket-range and total buckets less than 22."),

		    "Maximum latency (last bucket). Works only with --bucket-range."),

	OPT_PARENT(common_options),

	};

	const struct option profile_options[] = {
@@ -1751,7 +1761,22 @@ int cmd_ftrace(int argc, const char **argv) 
			ret = -EINVAL;

			goto out_delete_filters;

		}

		if (ftrace.bucket_range && !ftrace.max_latency) {

		if (ftrace.bucket_range && ftrace.max_latency &&

		    ftrace.max_latency < ftrace.min_latency + ftrace.bucket_range) {

			/* we need at least 1 bucket excluding min and max buckets */

			pr_err("--max-latency must be larger than min-latency + bucket-range\n");

			parse_options_usage(ftrace_usage, options,

					    "max-latency", /*short_opt=*/false);

			ret = -EINVAL;

			goto out_delete_filters;

		}

		/* set default unless max_latency is set and valid */

		ftrace.bucket_num = NUM_BUCKET;

		if (ftrace.bucket_range) {

			if (ftrace.max_latency)

				ftrace.bucket_num = (ftrace.max_latency - ftrace.min_latency) /

							ftrace.bucket_range + 2;

			else

				/* default max latency should depend on bucket range and num_buckets */

				ftrace.max_latency = (NUM_BUCKET - 2) * ftrace.bucket_range +

							ftrace.min_latency;

tools/perf/util/bpf_ftrace.c

+5 −1
Original line number Diff line number Diff line
@@ -39,6 +39,10 @@ int perf_ftrace__latency_prepare_bpf(struct perf_ftrace *ftrace) 


	skel->rodata->bucket_range = ftrace->bucket_range;

	skel->rodata->min_latency = ftrace->min_latency;

	skel->rodata->bucket_num = ftrace->bucket_num;

	if (ftrace->bucket_range && ftrace->bucket_num) {

		bpf_map__set_max_entries(skel->maps.latency, ftrace->bucket_num);

	}



	/* don't need to set cpu filter for system-wide mode */

	if (ftrace->target.cpu_list) {
@@ -138,7 +142,7 @@ int perf_ftrace__latency_read_bpf(struct perf_ftrace *ftrace __maybe_unused, 
	if (hist == NULL)

		return -ENOMEM;



	for (idx = 0; idx < NUM_BUCKET; idx++) {

	for (idx = 0; idx < skel->rodata->bucket_num; idx++) {

		err = bpf_map_lookup_elem(fd, &idx, hist);

		if (err) {

			buckets[idx] = 0;

tools/perf/util/bpf_skel/func_latency.bpf.c

+4 −3
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ const volatile int use_nsec = 0; 
const volatile unsigned int bucket_range;

const volatile unsigned int min_latency;

const volatile unsigned int max_latency;

const volatile unsigned int bucket_num = NUM_BUCKET;



SEC("kprobe/func")

int BPF_PROG(func_begin)
@@ -124,16 +125,16 @@ int BPF_PROG(func_end) 
			if (delta > 0) { // 1st entry: [ 1 unit .. bucket_range units )

				// clang 12 doesn't like s64 / u32 division

				key = (__u64)delta / bucket_range + 1;

				if (key >= NUM_BUCKET ||

				if (key >= bucket_num ||

					delta >= max_latency - min_latency)

					key = NUM_BUCKET - 1;

					key = bucket_num - 1;

			}



			delta += min_latency;

			goto do_lookup;

		}

		// calculate index using delta

		for (key = 0; key < (NUM_BUCKET - 1); key++) {

		for (key = 0; key < (bucket_num - 1); key++) {

			if (delta < (cmp_base << key))

				break;

		}

tools/perf/util/ftrace.h

+1 −0
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ struct perf_ftrace { 
	unsigned int		bucket_range;

	unsigned int		min_latency;

	unsigned int		max_latency;

	unsigned int		bucket_num;

	int			graph_depth;

	int			func_stack_trace;

	int			func_irq_info;