perf diff: Add weighted diff computation way to compare hist entries

Adding 'wdiff' as new computation way to compare hist entries.

If specified the 'Weighted diff' column is displayed with value 'd'
computed as:

   d = B->period * WEIGHT-A - A->period * WEIGHT-B

  - A/B being matching hist entry from first/second file specified
    (or perf.data/perf.data.old) respectively.
  - period being the hist entry period value
  - WEIGHT-A/WEIGHT-B being user suplied weights in the the '-c' option
    behind ':' separator like '-c wdiff:1,2'.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1349448287-18919-5-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-diff.txt

@@ -78,7 +78,7 @@ OPTIONS
 
 -c::
 --compute::
-        Differential computation selection - delta,ratio (default is delta).
+        Differential computation selection - delta,ratio,wdiff (default is delta).
         If '+' is specified as a first character, the output is sorted based
         on the computation results.
         See COMPARISON METHODS section for more info.
@@ -110,6 +110,19 @@ with:
 
   - period being the hist entry period value
 
+wdiff
+~~~~~
+If specified the 'Weighted diff' column is displayed with value 'd' computed as:
+
+   d = B->period * WEIGHT-A - A->period * WEIGHT-B
+
+  - A/B being matching hist entry from first/second file specified
+    (or perf.data/perf.data.old) respectively.
+
+  - period being the hist entry period value
+
+  - WEIGHT-A/WEIGHT-B being user suplied weights in the the '-c' option
+    behind ':' separator like '-c wdiff:1,2'.
 
 SEE ALSO
 --------