[tip:perfcounters/urgent] perf tools: callchain: Fix bad rounding of minimum rate

tip-bot for Frederic Weisbecker
2009-08-09T11:13:16Z

Commit-ID: c0a8865e32c8d1a562db38e06ef31ef23282f646
Gitweb: http://git.kernel.org/tip/c0a8865e32c8d1a562db38e06ef31ef23282f646
Author: Frederic Weisbecker <fweisbec@gmail.com>
AuthorDate: Sun, 9 Aug 2009 04:19:15 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sun, 9 Aug 2009 13:07:46 +0200

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 <mingo@elte.hu>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: acme@redhat.com
Cc: peterz@infradead.org
Cc: efault@gmx.de
LKML-Reference: <20090809024235.GA10146@nowhere>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
tools/perf/util/callchain.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index a8e67aa..0114734 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -13,6 +13,7 @@
#include <stdio.h>
#include <stdbool.h>
#include <errno.h>
+#include <math.h>

#include "callchain.h"

@@ -112,7 +113,7 @@ static void __sort_chain_graph_rel(struct callchain_node *node,
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);
@@ -126,7 +127,7 @@ static void
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;
}