perf ftrace latency: variable histogram buckets

The max-latency value can make the histogram smaller, but not larger, we
have a maximum of 22 buckets and specifying a max-latency that would
require more buckets has no effect.

Dynamically allocate the buckets and compute the bucket number from the
max latency as (max-min) / range + 2

If the maximum is not specified, we still set the bucket number to 22
and compute the maximum accordingly.

Fail if the maximum is smaller than min+range, this way we make sure we
always have 3 buckets: those below min, those above max and one in the
middle.

Since max-latency is not available in log2 mode, always use 22 buckets.

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/r/20250207080446.77630-1-gmonaco@redhat.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>