RE: [RFC PATCH v2 3/7] libperf: Add perf_evsel__{refresh, period}() functions

[nakamura.shun@xxxxxxxxxxx]

Hi jirka

> On Fri, Mar 25, 2022 at 01:38:25PM +0900, Shunsuke Nakamura wrote:
> 
> SNIP
> 
> > +int perf_evsel__refresh_cpu(struct perf_evsel *evsel, int refresh,
> > +int cpu_map_idx) {
> > +	return perf_evsel__run_ioctl(evsel, PERF_EVENT_IOC_REFRESH,
> refresh,
> > +cpu_map_idx); }
> > +
> > +int perf_evsel__refresh(struct perf_evsel *evsel, int refresh) {
> > +	int i;
> > +	int err = 0;
> > +
> > +	for (i = 0; i < xyarray__max_x(evsel->fd) && !err; i++)
> > +		err = perf_evsel__run_ioctl(evsel, PERF_EVENT_IOC_REFRESH,
> refresh, i);
> > +	return err;
> > +}
> > +
> > +int perf_evsel__period_cpu(struct perf_evsel *evsel, __u64 period,
> > +int cpu_map_idx) {
> > +	struct perf_event_attr *attr;
> > +	int err = 0;
> > +
> > +	attr = perf_evsel__attr(evsel);
> > +	if (!attr)
> > +		return -EINVAL;
> > +
> > +	err = perf_evsel__run_ioctl(evsel, PERF_EVENT_IOC_PERIOD,
> > +				    (unsigned long)&period, cpu_map_idx);
> > +	if (err)
> > +		return err;
> > +
> > +	attr->sample_period = period;
> 
> what's the point in updating attr? this will be used after event is created right?
> 
This is to maintain consistency between evsel->attr->sample_period and the sample_period of the created event.
Users can reference evsel->attr->sample_period using perf_evsel__attr().
So I thought it was necessary to update the sample_period of the event and the sample_period of evsel to avoid discrepancies.


Best Regards
Shunsuke