Commit c0a8865e authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: acme@redhat.com
Cc: peterz@infradead.org
Cc: efault@gmx.de
LKML-Reference: <20090809024235.GA10146@nowhere>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 183f3b08
......@@ -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;
}
......
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment