perf report: Speed up exit path

When cmd_record exits the whole perf binary will exit right after,
so no need to traverse lots of complex data structures freeing them.

Sticked a comment for leak detectives and for a experiment with obstacks
to be performed so that we can speed up freeing that memory.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -348,7 +348,18 @@ static int __cmd_report(void)
 		hists__tty_browse_tree(&session->hists_tree, help);
 
 out_delete:
-	perf_session__delete(session);
+	/*
+	 * Speed up the exit process, for large files this can
+	 * take quite a while.
+	 *
+	 * XXX Enable this when using valgrind or if we ever
+	 * librarize this command.
+	 *
+	 * Also experiment with obstacks to see how much speed
+	 * up we'll get here.
+	 *
+ 	 * perf_session__delete(session);
+ 	 */
 	return ret;
 }