Commit 690a052a authored by Gabriele Monaco's avatar Gabriele Monaco Committed by Arnaldo Carvalho de Melo
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perf ftrace latency: Add --max-latency option 



This patch adds a max-latency option as discussed, in case the number of
buckets is more than 22, we don't observe the setting (for now, let's
say).

By default or if 0 is passed, the value is automatically determined
based on the number of buckets, range and minimum, so that we fill all
available buffers (equivalent to the behaviour before this patch).

We now get something like this:

  # perf ftrace latency --bucket-range=20 \
			--min-latency 10 \
			--max-latency=100 \
			-T switch_mm_irqs_off -a sleep 2
  #   DURATION     |      COUNT | GRAPH             |
       0 -   10 us |       1731 | ################  |
      10 -   30 us |          1 |                   |
      30 -   50 us |          0 |                   |
      50 -   70 us |          0 |                   |
      70 -   90 us |          0 |                   |
      90 -  100 us |          0 |                   |
     100 -  ... us |          0 |                   |

Note the maximum is observed also if it doesn't cover completely a full
range (the second to last range is 10us long to let the last start at
100 sharp), this looks to me more sensible and eases the computations,
since we don't need to account for the range while filling the buckets.

Signed-off-by: default avatarGabriele Monaco <gmonaco@redhat.com>
Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20241112181214.1171244-5-acme@kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 08b875b6

tools/perf/Documentation/perf-ftrace.txt

+4 −0
Original line number Diff line number Diff line
@@ -155,6 +155,10 @@ OPTIONS for 'perf ftrace latency' 
	Minimum latency for the start of the first bucket, in ms or ns (according to

	-n/--use-nsec).



--max-latency=::

	Maximum latency for the start of the last bucket, in ms or ns (according to

	-n/--use-nsec). The setting is ignored if the value results in more than

	22 buckets.



OPTIONS for 'perf ftrace profile'

---------------------------------

tools/perf/builtin-ftrace.c

+25 −3
Original line number Diff line number Diff line
@@ -730,6 +730,7 @@ static void make_histogram(struct perf_ftrace *ftrace, int buckets[], 
			   char *buf, size_t len, char *linebuf)

{

	int min_latency = ftrace->min_latency;

	int max_latency = ftrace->max_latency;

	char *p, *q;

	char *unit;

	double num;
@@ -794,7 +795,7 @@ 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 (i >= NUM_BUCKET)

		if (i >= NUM_BUCKET || num >= max_latency - min_latency)

			i = NUM_BUCKET - 1;



do_inc:
@@ -837,7 +838,7 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
	       buckets[0], bar_len, bar, bar_total - bar_len, "");



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

		int start, stop;

		unsigned int start, stop;

		const char *unit = use_nsec ? "ns" : "us";



		if (!ftrace->bucket_range) {
@@ -853,6 +854,11 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
			start = (i - 1) * ftrace->bucket_range + min_latency;

			stop  = i * ftrace->bucket_range + min_latency;



			if (start >= ftrace->max_latency)

				break;

			if (stop > ftrace->max_latency)

				stop = ftrace->max_latency;



			if (start >= 1000) {

				double dstart = start / 1000.0,

				       dstop  = stop / 1000.0;
@@ -873,7 +879,9 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[]) 
	if (!ftrace->bucket_range) {

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

	} else {

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

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

		if (upper_outlier > ftrace->max_latency)

			upper_outlier = ftrace->max_latency;



		if (upper_outlier >= 1000) {

			double dstart = upper_outlier / 1000.0;
@@ -1609,6 +1617,8 @@ int cmd_ftrace(int argc, const char **argv) 
		    "Bucket range in ms or ns (-n/--use-nsec), default is log2() mode"),

	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."),

	OPT_PARENT(common_options),

	};

	const struct option profile_options[] = {
@@ -1715,6 +1725,18 @@ int cmd_ftrace(int argc, const char **argv) 
			/* default min latency should be the bucket range */

			ftrace.min_latency = ftrace.bucket_range;

		}

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

			pr_err("--max-latency works only with --bucket-range\n");

			parse_options_usage(ftrace_usage, options,

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

			ret = -EINVAL;

			goto out_delete_filters;

		}

		if (!ftrace.max_latency) {

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

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

						ftrace.min_latency;

		}

		cmd_func = __cmd_latency;

		break;

	case PERF_FTRACE_PROFILE:

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

+3 −1
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ const volatile int has_task = 0; 
const volatile int use_nsec = 0;

const volatile unsigned int bucket_range;

const volatile unsigned int min_latency;

const volatile unsigned int max_latency;



SEC("kprobe/func")

int BPF_PROG(func_begin)
@@ -116,7 +117,8 @@ int BPF_PROG(func_end) 
			// than the min latency desired.

			if (delta > 0) { // 1st entry: [ 1 unit .. bucket_range units )

				key = delta / bucket_range + 1;

				if (key >= NUM_BUCKET)

				if (key >= NUM_BUCKET ||

					delta >= max_latency - min_latency)

					key = NUM_BUCKET - 1;

			}

			goto do_lookup;

tools/perf/util/ftrace.h

+1 −0
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ struct perf_ftrace { 
	bool			use_nsec;

	unsigned int		bucket_range;

	unsigned int		min_latency;

	unsigned int		max_latency;

	int			graph_depth;

	int			func_stack_trace;

	int			func_irq_info;