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>
c0a8865e32