perf symbols: Add front end cache for DSO symbol lookup

Acked-by: David Ahern <dsahern@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-voo94tow8wpkcc76mlkny6sc@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/dso.h

@@ -137,6 +137,10 @@ struct dso {
 	struct rb_node	 rb_node;	/* rbtree node sorted by long name */
 	struct rb_root	 symbols[MAP__NR_TYPES];
 	struct rb_root	 symbol_names[MAP__NR_TYPES];
+	struct {
+		u64		addr;
+		struct symbol	*symbol;
+	} last_find_result[MAP__NR_TYPES];
 	void		 *a2l;
 	char		 *symsrc_filename;
 	unsigned int	 a2l_fails;

tools/perf/util/symbol.c

@@ -444,7 +444,12 @@ static struct symbol *symbols__find_by_name(struct rb_root *symbols,
 struct symbol *dso__find_symbol(struct dso *dso,
 				enum map_type type, u64 addr)
 {
-	return symbols__find(&dso->symbols[type], addr);
+	if (dso->last_find_result[type].addr != addr) {
+		dso->last_find_result[type].addr   = addr;
+		dso->last_find_result[type].symbol = symbols__find(&dso->symbols[type], addr);
+	}
+
+	return dso->last_find_result[type].symbol;
 }
 
 struct symbol *dso__first_symbol(struct dso *dso, enum map_type type)