To improve 'perf diff', implement a --time filter option to diff the
samples within given time window.

It supports time percent with multiple time ranges. The time string
format is 'a%/n,b%/m,...' or 'a%-b%,c%-%d,...'.

For example:

Select the second 10% time slice to diff:

  perf diff --time 10%/2

Select from 0% to 10% time slice to diff:

  perf diff --time 0%-10%

Select the first and the second 10% time slices to diff:

  perf diff --time 10%/1,10%/2

Select from 0% to 10% and 30% to 40% slices to diff:

  perf diff --time 0%-10%,30%-40%

It also supports analysing samples within a given time window
<start>,<stop>.

Times have the format seconds.microseconds.

If 'start' is not given (i.e., time string is ',x.y') then analysis starts at
the beginning of the file.

If the stop time is not given (i.e, time string is 'x.y,') then analysis
goes to end of file.

Time string is 'a1.b1,c1.d1:a2.b2,c2.d2'. Use ':' to separate timestamps for
different perf.data files.

For example, we get the timestamp information from perf script.

  perf script -i perf.data.old

    mgen 13940 [000]  3946.361400: ...

  perf script -i perf.data

    mgen 13940 [000]  3971.150589 ...

  perf diff --time 3946.361400,:3971.150589,

It analyzes the perf.data.old from the timestamp 3946.361400 to the end of
perf.data.old and analyzes the perf.data from the timestamp 3971.150589 to the
end of perf.data.

 v4:
 ---
 Update abstime_str_dup(), let it return error if strdup
 is failed, and update __cmd_diff() accordingly.
Signed-off-by: Jin Yao <yao.jin@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: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1551791143-10334-2-git-send-email-yao.jin@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>