Commit b09c2364 authored by Arnaldo Carvalho de Melo's avatar Arnaldo Carvalho de Melo
Browse files

perf record: Throttle user defined frequencies to the maximum allowed 



  # 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: default avatarIngo 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 7831bf23

tools/perf/Documentation/perf-record.txt

+6 −1
Original line number Diff line number Diff line
@@ -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=::

tools/perf/builtin-record.c

+2 −0
Original line number Diff line number Diff line
@@ -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),

tools/perf/perf.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

tools/perf/util/record.c

+15 −5
Original line number Diff line number Diff line
@@ -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"

		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;

		}

	}



	/*

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