Currently print count interval for performance counters values is
limited by 10ms so reading the values at frequencies higher than 100Hz
is restricted by the tool.

This change makes perf stat -I possible on frequencies up to 1KHz and,
to some extent, makes perf stat -I to be on-par with perf record
sampling profiling.

When running perf stat -I for monitoring e.g. PCIe uncore counters and
at the same time profiling some I/O workload by perf record e.g. for
cpu-cycles and context switches, it is then possible to observe
consolidated CPU/OS/IO(Uncore) performance picture for that workload.

Tool overhead warning printed when specifying -v option can be missed
due to screen scrolling in case you have output to the console
so message is moved into help available by running perf stat -h.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/b842ad6a-d606-32e4-afe5-974071b5198e@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>