perf session: Change add_hist_entry to take the tree root instead of session

In order to minimize the impact of storing multiple events in a
report this function will now take the root of the histogram
tree so that the logic for selecting the proper tree can be
inserted before the call.

Signed-off-by: Eric B Munson <ebmunson@us.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1267804269-22660-3-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index 18b3f50..20df735 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -26,7 +26,8 @@
 					struct addr_location *al, u64 count)
 {
 	bool hit;
-	struct hist_entry *he = __perf_session__add_hist_entry(self, al, NULL,
+	struct hist_entry *he = __perf_session__add_hist_entry(&self->hists,
+							       al, NULL,
 							       count, &hit);
 	if (he == NULL)
 		return -ENOMEM;