tree ef8566f22145f433806f62fc7eaf7817cea486a5
parent 4f67336870f641daa485ea504777486e24a9aece
author Arnaldo Carvalho de Melo <acme@redhat.com> 1519922783 -0300
committer Arnaldo Carvalho de Melo <acme@redhat.com> 1520254723 -0300

perf record: Allow asking for the maximum allowed sample rate

Add the handy '-F max' shortcut to reading and using the
kernel.perf_event_max_sample_rate value as the user supplied
sampling frequency:

  # perf record -F max sleep 1
  info: Using a maximum frequency rate of 15,000 Hz
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.019 MB perf.data (14 samples) ]
  # sysctl kernel.perf_event_max_sample_rate
  kernel.perf_event_max_sample_rate = 15000
  # 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

  # perf record -F 10 sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.019 MB perf.data (4 samples) ]
  # perf evlist -v
  cycles:ppp: size: 112, { sample_period, sample_freq }: 10, 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
  #

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-4y0tiuws62c64gp4cf0hme0m@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>