perf diff: Print diff result more precisely

Current perf diff result is somewhat confusing since it sometimes hide
small result and sometimes there's no result.  So do not hide small
result (less than 0.01%) and print "N/A" if baseline is not
recorded (for ratio and wdiff only).  Blank means the baseline is
available but its pairs are not.

Before:

  # Baseline    Delta  Shared Object      Symbol
  # ........  .......  .................  .........................
  #
       ...
       0.01%   -0.01%  [kernel.kallsyms]  [k] native_write_msr_safe
       0.01%           [kernel.kallsyms]  [k] scheduler_tick
       0.01%           [kernel.kallsyms]  [k] native_read_msr_safe
       0.00%           [kernel.kallsyms]  [k] __rcu_read_unlock
                       [kernel.kallsyms]  [k] _raw_spin_lock
               +0.01%  [kernel.kallsyms]  [k] apic_timer_interrupt
                       [kernel.kallsyms]  [k] read_tsc

After:

  # Baseline    Delta  Shared Object      Symbol
  # ........  .......  .................  .........................
  #
       ...
       0.01%   -0.01%  [kernel.kallsyms]  [k] native_write_msr_safe
       0.01%           [kernel.kallsyms]  [k] scheduler_tick
       0.01%           [kernel.kallsyms]  [k] native_read_msr_safe
       0.00%           [kernel.kallsyms]  [k] __rcu_read_unlock
               +0.01%  [kernel.kallsyms]  [k] _raw_spin_lock
               +0.01%  [kernel.kallsyms]  [k] apic_timer_interrupt
               +0.01%  [kernel.kallsyms]  [k] read_tsc

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1419656793-32756-3-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-diff.c

@@ -788,7 +788,7 @@ static int __hpp__color_compare(struct perf_hpp_fmt *fmt,
 	char pfmt[20] = " ";
 
 	if (!pair)
-		goto dummy_print;
+		goto no_print;
 
 	switch (comparison_method) {
 	case COMPUTE_DELTA:
@@ -797,8 +797,6 @@ static int __hpp__color_compare(struct perf_hpp_fmt *fmt,
 		else
 			diff = compute_delta(he, pair);
 
-		if (fabs(diff) < 0.01)
-			goto dummy_print;
 		scnprintf(pfmt, 20, "%%%+d.2f%%%%", dfmt->header_width - 1);
 		return percent_color_snprintf(hpp->buf, hpp->size,
 					pfmt, diff);
@@ -829,6 +827,9 @@ static int __hpp__color_compare(struct perf_hpp_fmt *fmt,
 		BUG_ON(1);
 	}
 dummy_print:
+	return scnprintf(hpp->buf, hpp->size, "%*s",
+			dfmt->header_width, "N/A");
+no_print:
 	return scnprintf(hpp->buf, hpp->size, "%*s",
 			dfmt->header_width, pfmt);
 }
@@ -879,14 +880,15 @@ hpp__entry_pair(struct hist_entry *he, struct hist_entry *pair,
 		else
 			diff = compute_delta(he, pair);
 
-		if (fabs(diff) >= 0.01)
+		scnprintf(buf, size, "%+4.2F%%", diff);
-			scnprintf(buf, size, "%+4.2F%%", diff);
 		break;
 
 	case PERF_HPP_DIFF__RATIO:
 		/* No point for ratio number if we are dummy.. */
-		if (he->dummy)
+		if (he->dummy) {
+			scnprintf(buf, size, "N/A");
 			break;
+		}
 
 		if (pair->diff.computed)
 			ratio = pair->diff.period_ratio;
@@ -899,8 +901,10 @@ hpp__entry_pair(struct hist_entry *he, struct hist_entry *pair,
 
 	case PERF_HPP_DIFF__WEIGHTED_DIFF:
 		/* No point for wdiff number if we are dummy.. */
-		if (he->dummy)
+		if (he->dummy) {
+			scnprintf(buf, size, "N/A");
 			break;
+		}
 
 		if (pair->diff.computed)
 			wdiff = pair->diff.wdiff;