perf annotate: Add number of samples to the header

Staring at annotations of large functions is useless if there's only a
few samples in them. Report the number of samples in the header to make
this easier to determine.

Committer note:

The change amounts to:

  - Percent | Source code & Disassembly of perf-vdso.so for cycles:u
  ------------------------------------------------------------------
  + Percent | Source code & Disassembly of perf-vdso.so for cycles:u (3278 samples)
  +--------------------------------------------------------------------------------
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20160630082955.GA30921@twins.programming.kicks-ass.net
[ split from a larger patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/annotate.c

@@ -1522,6 +1522,7 @@ int symbol__annotate_printf(struct symbol *sym, struct map *map,
 	const char *d_filename;
 	const char *evsel_name = perf_evsel__name(evsel);
 	struct annotation *notes = symbol__annotation(sym);
+	struct sym_hist *h = annotation__histogram(notes, evsel->idx);
 	struct disasm_line *pos, *queue = NULL;
 	u64 start = map__rip_2objdump(map, sym->start);
 	int printed = 2, queue_len = 0;
@@ -1544,8 +1545,8 @@ int symbol__annotate_printf(struct symbol *sym, struct map *map,
 	if (perf_evsel__is_group_event(evsel))
 		width *= evsel->nr_members;
 
-	graph_dotted_len = printf(" %-*.*s|	Source code & Disassembly of %s for %s\n",
-	       width, width, "Percent", d_filename, evsel_name);
+	graph_dotted_len = printf(" %-*.*s|	Source code & Disassembly of %s for %s (%" PRIu64 " samples)\n",
+	       width, width, "Percent", d_filename, evsel_name, h->sum);
 
 	printf("%-*.*s----\n",
 	       graph_dotted_len, graph_dotted_len, graph_dotted_line);