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: Ingo Molnar <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Wang Nan <[email protected]>
Link: https://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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