On Sat, 2012-10-20 at 16:33 +0200, Jiri Olsa wrote:
> It's possible some of the counters in the group could be
> disabled when sampling member of the event group is reading
> the rest via PERF_SAMPLE_READ sample type processing. Disabled
> counters could then produce wrong numbers.
>
> Fixing that by reading only enabled counters for PERF_SAMPLE_READ
> sample type processing.
>
However did you run into this?
> ---
> kernel/events/core.c | 18 +++++++++++++++---
> 1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 32aec40..5220d01 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4012,12 +4012,24 @@ static void perf_output_read_group(struct
> perf_output_handle *handle,
> __output_copy(handle, values, n * sizeof(u64));
>
> list_for_each_entry(sub, &leader->sibling_list, group_entry) {
> + u64 value = 0;
> n = 0;
>
> - if (sub != event)
> - sub->pmu->read(sub);
> + /*
> + * We are NOT interested in disabled counters,
> + * giving us strange values and keeping us from
> + * good night sleep!!!
> + */
> + if (sub->state > PERF_EVENT_STATE_OFF) {
> +
superfluous whitespace there... ;-)
> + if (sub != event)
> + sub->pmu->read(sub);
> +
> + value = perf_event_count(sub);
> + }
> +
> + values[n++] = value;
>
> - values[n++] = perf_event_count(sub);
> if (read_format & PERF_FORMAT_ID)
> values[n++] = primary_event_id(sub);
>
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