[PATCH 12/28] perf record: Throttle user defined frequencies to the maximum allowed

Arnaldo Carvalho de Melo
2018-03-05T14:30:55Z

From: Arnaldo Carvalho de Melo <acme@redhat.com>

# perf record -F 200000 sleep 1
warning: Maximum frequency rate (15,000 Hz) exceeded, throttling from 200,000 Hz to 15,000 Hz.
The limit can be raised via /proc/sys/kernel/perf_event_max_sample_rate.
The kernel will lower it when perf's interrupts take too long.
Use --strict-freq to disable this throttling, refusing to record.
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.019 MB perf.data (15 samples) ]
# perf evlist -v
cycles:ppp: size: 112, { sample_period, sample_freq }: 15000, sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1

For those wanting that it fails if the desired frequency can't be used:

# perf record --strict-freq -F 200000 sleep 1
error: Maximum frequency rate (15,000 Hz) exceeded.
Please use -F freq option with a lower value or consider
tweaking /proc/sys/kernel/perf_event_max_sample_rate.
#

Suggested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-oyebruc44nlja499nqkr1nzn@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/Documentation/perf-record.txt | 7 ++++++-
tools/perf/builtin-record.c | 2 ++
tools/perf/perf.h | 1 +
tools/perf/util/record.c | 20 +++++++++++++++-----
4 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 94f2faebc7f0..cc37b3a4be76 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -191,11 +191,16 @@ OPTIONS
-i::
--no-inherit::
Child tasks do not inherit counters.
+
-F::
--freq=::
Profile at this frequency. Use 'max' to use the currently maximum
allowed frequency, i.e. the value in the kernel.perf_event_max_sample_rate
- sysctl.
+ sysctl. Will throttle down to the currently maximum allowed frequency.
+ See --strict-freq.
+
+--strict-freq::
+ Fail if the specified frequency can't be used.

-m::
--mmap-pages=::
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index e1821eea14ef..62387942a1d5 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1543,6 +1543,8 @@ static struct option __record_options[] = {
OPT_BOOLEAN(0, "tail-synthesize", &record.opts.tail_synthesize,
"synthesize non-sample events at the end of output"),
OPT_BOOLEAN(0, "overwrite", &record.opts.overwrite, "use overwrite mode"),
+ OPT_BOOLEAN(0, "strict-freq", &record.opts.strict_freq,
+ "Fail if the specified frequency can't be used"),
OPT_CALLBACK('F', "freq", &record.opts, "freq or 'max'",
"profile at this frequency",
record__parse_freq),
diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index a5df8bf73a68..007e0dfd5ce3 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -61,6 +61,7 @@ struct record_opts {
bool tail_synthesize;
bool overwrite;
bool ignore_missing_thread;
+ bool strict_freq;
unsigned int freq;
unsigned int mmap_pages;
unsigned int auxtrace_mmap_pages;
diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index acabf54ceccb..4f1a82e76d39 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -216,11 +216,21 @@ static int record_opts__config_freq(struct record_opts *opts)
* User specified frequency is over current maximum.
*/
if (user_freq && (max_rate < opts->freq)) {
- pr_err("Maximum frequency rate (%u) reached.\n"
- "Please use -F freq option with lower value or consider\n"
- "tweaking /proc/sys/kernel/perf_event_max_sample_rate.\n",
- max_rate);
- return -1;
+ if (opts->strict_freq) {
+ pr_err("error: Maximum frequency rate (%'u Hz) exceeded.\n"
+ " Please use -F freq option with a lower value or consider\n"
+ " tweaking /proc/sys/kernel/perf_event_max_sample_rate.\n",
+ max_rate);
+ return -1;
+ } else {
+ pr_warning("warning: Maximum frequency rate (%'u Hz) exceeded, throttling from %'u Hz to %'u Hz.\n"
+ " The limit can be raised via /proc/sys/kernel/perf_event_max_sample_rate.\n"
+ " The kernel will lower it when perf's interrupts take too long.\n"
+ " Use --strict-freq to disable this throttling, refusing to record.\n",
+ max_rate, opts->freq, max_rate);
+
+ opts->freq = max_rate;
+ }
}

/*
--
2.14.3