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perf ftrace latency: Introduce --min-latency to narrow down into a latency range

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Things below and over will be in the first and last, outlier, buckets.

Without it:

  # perf ftrace latency --use-nsec --use-bpf \
			--bucket-range=200 \
			-T switch_mm_irqs_off -a sleep 2
  #   DURATION     |      COUNT | GRAPH                                   |
       0 -  200 ns |          0 |                                         |
     200 -  400 ns |         44 |                                         |
     400 -  600 ns |        291 | #                                       |
     600 -  800 ns |        506 | ##                                      |
     800 - 1000 ns |        148 |                                         |
    1.00 - 1.20 us |        581 | ##                                      |
    1.20 - 1.40 us |       2199 | ##########                              |
    1.40 - 1.60 us |       1048 | ####                                    |
    1.60 - 1.80 us |       1448 | ######                                  |
    1.80 - 2.00 us |       1091 | #####                                   |
    2.00 - 2.20 us |        517 | ##                                      |
    2.20 - 2.40 us |        318 | #                                       |
    2.40 - 2.60 us |        370 | #                                       |
    2.60 - 2.80 us |        271 | #                                       |
    2.80 - 3.00 us |        150 |                                         |
    3.00 - 3.20 us |         85 |                                         |
    3.20 - 3.40 us |         48 |                                         |
    3.40 - 3.60 us |         40 |                                         |
    3.60 - 3.80 us |         22 |                                         |
    3.80 - 4.00 us |         13 |                                         |
    4.00 - 4.20 us |         14 |                                         |
    4.20 - ...  us |        626 | ##                                      |
  #
  # perf ftrace latency --use-nsec --use-bpf \
			--bucket-range=20 --min-latency=1200 \
			-T switch_mm_irqs_off -a sleep 2
  #   DURATION     |      COUNT | GRAPH                                   |
       0 - 1200 ns |       1243 | #####                                   |
    1.20 - 1.22 us |        141 |                                         |
    1.22 - 1.24 us |        202 |                                         |
    1.24 - 1.26 us |        209 |                                         |
    1.26 - 1.28 us |        219 |                                         |
    1.28 - 1.30 us |        208 |                                         |
    1.30 - 1.32 us |        245 | #                                       |
    1.32 - 1.34 us |        246 | #                                       |
    1.34 - 1.36 us |        224 | #                                       |
    1.36 - 1.38 us |        219 |                                         |
    1.38 - 1.40 us |        206 |                                         |
    1.40 - 1.42 us |        190 |                                         |
    1.42 - 1.44 us |        190 |                                         |
    1.44 - 1.46 us |        146 |                                         |
    1.46 - 1.48 us |        140 |                                         |
    1.48 - 1.50 us |        125 |                                         |
    1.50 - 1.52 us |        115 |                                         |
    1.52 - 1.54 us |        102 |                                         |
    1.54 - 1.56 us |         87 |                                         |
    1.56 - 1.58 us |         90 |                                         |
    1.58 - 1.60 us |         85 |                                         |
    1.60 - ...  us |       5487 | ########################                |
  #

Now we want focus on the latencies starting at 1.2us, with a finer
grained range of 20ns:

This is all on a live system, so statistically interesting, but not
narrowing down on the same numbers, so a 'perf ftrace latency record'
seems interesting to then use all on the same snapshot of latencies.

A --max-latency counterpart should come next, at first limiting the
max-latency to 20 * bucket-size, as we have a fixed buckets array with
20 + 2 entries (+ for the outliers) and thus would need to make it
larger for higher latencies.

We also may need a way to ask for not considering the out of range
values (first and last buckets) when drawing the buckets bars.

Co-developed-by: Gabriele Monaco <gmonaco@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/20241112181214.1171244-4-acme@kernel.org
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo 2024-11-12 15:12:13 -03:00
parent e8536dd47a
commit 08b875b6bf
5 changed files with 43 additions and 7 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
tools/perf/Documentation/perf-ftrace.txt
View file

@ -151,6 +151,10 @@ OPTIONS for 'perf ftrace latency'
--bucket-range=::
Bucket range in ms or ns (according to -n/--use-nsec), default is log2() mode.
--min-latency=::
Minimum latency for the start of the first bucket, in ms or ns (according to
-n/--use-nsec).
OPTIONS for 'perf ftrace profile'
---------------------------------

32
tools/perf/builtin-ftrace.c
View file

@ -729,6 +729,7 @@ out:
static void make_histogram(struct perf_ftrace *ftrace, int buckets[],
char *buf, size_t len, char *linebuf)
{
int min_latency = ftrace->min_latency;
char *p, *q;
char *unit;
double num;
@ -777,6 +778,12 @@ static void make_histogram(struct perf_ftrace *ftrace, int buckets[],
if (ftrace->use_nsec)
num *= 1000;
i = 0;
if (num < min_latency)
goto do_inc;
num -= min_latency;
if (!ftrace->bucket_range) {
i = log2(num);
if (i < 0)
@ -784,13 +791,13 @@ static void make_histogram(struct perf_ftrace *ftrace, int buckets[],
} else {
// Less than 1 unit (ms or ns), or, in the future,
// than the min latency desired.
i = 0;
if (num > 0) // 1st entry: [ 1 unit .. bucket_range units ]
i = num / ftrace->bucket_range + 1;
}
if (i >= NUM_BUCKET)
i = NUM_BUCKET - 1;
do_inc:
buckets[i]++;
next:
@ -804,6 +811,7 @@ next:
static void display_histogram(struct perf_ftrace *ftrace, int buckets[])
{
int min_latency = ftrace->min_latency;
bool use_nsec = ftrace->use_nsec;
int i;
int total = 0;
@ -825,7 +833,8 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[])
bar_len = buckets[0] * bar_total / total;
printf(" %4d - %4d %s | %10d | %.*s%*s |\n",
0, 1, use_nsec ? "ns" : "us", buckets[0], bar_len, bar, bar_total - bar_len, "");
0, min_latency, use_nsec ? "ns" : "us",
buckets[0], bar_len, bar, bar_total - bar_len, "");
for (i = 1; i < NUM_BUCKET - 1; i++) {
int start, stop;
@ -841,8 +850,8 @@ static void display_histogram(struct perf_ftrace *ftrace, int buckets[])
unit = use_nsec ? "us" : "ms";
}
} else {
start = (i - 1) * ftrace->bucket_range + 1;
stop = i * ftrace->bucket_range + 1;
start = (i - 1) * ftrace->bucket_range + min_latency;
stop = i * ftrace->bucket_range + min_latency;
if (start >= 1000) {
double dstart = start / 1000.0,
@ -864,7 +873,7 @@ print_bucket_info:
if (!ftrace->bucket_range) {
printf(" %4d - %-4s %s", 1, "...", use_nsec ? "ms" : "s ");
} else {
int upper_outlier = (NUM_BUCKET - 2) * ftrace->bucket_range;
int upper_outlier = (NUM_BUCKET - 2) * ftrace->bucket_range + min_latency;
if (upper_outlier >= 1000) {
double dstart = upper_outlier / 1000.0;
@ -1598,6 +1607,8 @@ int cmd_ftrace(int argc, const char **argv)
"Use nano-second histogram"),
OPT_UINTEGER(0, "bucket-range", &ftrace.bucket_range,
"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_PARENT(common_options),
};
const struct option profile_options[] = {
@ -1693,6 +1704,17 @@ int cmd_ftrace(int argc, const char **argv)
ret = -EINVAL;
goto out_delete_filters;
}
if (!ftrace.bucket_range && ftrace.min_latency) {
pr_err("--min-latency works only with --bucket-range\n");
parse_options_usage(ftrace_usage, options,
"min-latency", /*short_opt=*/false);
ret = -EINVAL;
goto out_delete_filters;
}
if (!ftrace.min_latency) {
/* default min latency should be the bucket range */
ftrace.min_latency = ftrace.bucket_range;
}
cmd_func = __cmd_latency;
break;
case PERF_FTRACE_PROFILE:

1
tools/perf/util/bpf_ftrace.c
View file

@ -37,6 +37,7 @@ int perf_ftrace__latency_prepare_bpf(struct perf_ftrace *ftrace)
}
skel->rodata->bucket_range = ftrace->bucket_range;
skel->rodata->min_latency = ftrace->min_latency;
/* don't need to set cpu filter for system-wide mode */
if (ftrace->target.cpu_list) {

12
tools/perf/util/bpf_skel/func_latency.bpf.c
View file

@ -42,6 +42,7 @@ const volatile int has_cpu = 0;
const volatile int has_task = 0;
const volatile int use_nsec = 0;
const volatile unsigned int bucket_range;
const volatile unsigned int min_latency;
SEC("kprobe/func")
int BPF_PROG(func_begin)
@ -93,7 +94,7 @@ int BPF_PROG(func_end)
start = bpf_map_lookup_elem(&functime, &tid);
if (start) {
__s64 delta = bpf_ktime_get_ns() - *start;
__u32 key;
__u32 key = 0;
__u64 *hist;
bpf_map_delete_elem(&functime, &tid);
@ -103,9 +104,16 @@ int BPF_PROG(func_end)
if (bucket_range != 0) {
delta /= cmp_base;
if (min_latency > 0) {
if (delta > min_latency)
delta -= min_latency;
else
goto do_lookup;
}
// Less than 1 unit (ms or ns), or, in the future,
// than the min latency desired.
key = 0;
if (delta > 0) { // 1st entry: [ 1 unit .. bucket_range units )
key = delta / bucket_range + 1;
if (key >= NUM_BUCKET)

1
tools/perf/util/ftrace.h
View file

@ -21,6 +21,7 @@ struct perf_ftrace {
bool inherit;
bool use_nsec;
unsigned int bucket_range;
unsigned int min_latency;
int graph_depth;
int func_stack_trace;
int func_irq_info;