perf hists: clear dummy entry accumulated period

From: Kan Liang <[email protected]>

The accumulated period for dummy entry should also be 0. Otherwise, the total overhead could be overcounted.
[perf]$ perf record -e '{LLC-load-misses,cpu/instructions/}' --call-graph=lbr ./tchain
[perf]$ perf report --stdio
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 21K of event 'anon group { LLC-load-misses, cpu/instructions/ }'
# Event count (approx.): 16313667937
#
# Children Self Command Shared Object
Symbol

 # ................  ................  ...........  ................
 ............................
 #
   4769.98%   0.01%     0.00%   0.01%  tchain_edit  [kernel.vmlinux]
 [k] update_fast_timekeeper
   4356.18%   0.01%     0.00%   0.01%  tchain_edit  [kernel.vmlinux]
 [k] trigger_load_balance
   3181.12%   0.01%     0.00%   0.01%  tchain_edit  [kernel.vmlinux]
 [k] irq_work_tick
   1592.37%   0.00%     0.00%   0.00%  tchain_edit  [kernel.vmlinux]
 [k] cpu_needs_another_gp

---
 tools/perf/util/hist.c | 1 +
 1 file changed, 1 insertion(+)

index 991a351..657d1ca 100644
@@ -2062,6 +2062,7 @@ static struct hist_entry *hists__add_dummy_entry(struct hists *hists,
 	if (he) {
 		memset(&he->stat, 0, sizeof(he->stat));
 		he->hists = hists;
+		memset(he->stat_acc, 0, sizeof(he->stat));
 		rb_link_node(&he->rb_node_in, parent, p);
 		rb_insert_color(&he->rb_node_in, root);
 		hists__inc_stats(hists, he);

2.5.0