perf tools: callchain: Fix bad rounding of minimum rate

Sometimes we get callchain branches that have a rate under the
limit given by the user.

Say you launched:

perf record -f -g -a ./hackbench 10
perf report -g fractal,10.0

And you got:

2.33% hackbench [kernel] [k] _spin_lock_irqsave
|
|--78.57%-- remove_wait_queue
| poll_freewait
| do_sys_poll
| sys_poll
| sysenter_dispatch
| 0xf7ffa430
| 0x1ffadea3c
|
|--7.14%-- __up_read
| up_read
| do_page_fault
| page_fault
| 0xf7ffa430
| 0xa0df710000000a
...

It is abnormal to get a 7.14% branch whereas we passed a 10%
filter.

The problem is that we round down the minimum threshold. This
happens mostly when we have very low number of events. If the
total amount of your branch is 4 and you have a subranch of 3
events, filtering to 90% will be computed like follows:

limit = 4 * 0.9;

The result is about 3.6, but the cast to integer will round
down to 3. It means that our filter is actually of 75%

We must then explicitly round up the minimum threshold.

Reported-by: Ingo Molnar <[e-mail]>
Signed-off-by: Frederic Weisbecker <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
LKML-Reference: <20090809024235.GA10146@nowhere>
Signed-off-by: Ingo Molnar <[e-mail]>

tools/perf/util/callchain.c

···
 #include <stdio.h>
 #include <stdbool.h>
 #include <errno.h>
+#include <math.h>
 
 #include "callchain.h"
 
···
 	u64 min_hit;
 
 	node->rb_root = RB_ROOT;
-	min_hit = node->children_hit * min_percent / 100.0;
+	min_hit = ceil(node->children_hit * min_percent);
 
 	chain_for_each_child(child, node) {
 		__sort_chain_graph_rel(child, min_percent);
···
 sort_chain_graph_rel(struct rb_root *rb_root, struct callchain_node *chain_root,
 		     u64 min_hit __used, struct callchain_param *param)
 {
-	__sort_chain_graph_rel(chain_root, param->min_percent);
+	__sort_chain_graph_rel(chain_root, param->min_percent / 100.0);
 	rb_root->rb_node = chain_root->rb_root.rb_node;
 }