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SubjectRe: [PATCH 1/3] perf tools: Put proper period for for samples without PERIOD sample_type
On Wed, Feb 05, 2014 at 10:27:30AM +0900, Namhyung Kim wrote:
> Hi Jiri,
>
> On Mon, 3 Feb 2014 12:44:41 +0100, Jiri Olsa wrote:
> > We use PERF_SAMPLE_PERIOD sample type only for frequency
> > setup -F (default) option. The -c does not need store period,
> > because it's always the same.
> >
> > In -c case the report code uses '1' as period. Fixing
> > it to perf_event_attr::sample_period.
>
> All 3 patches look good. But I found something strange. When we
> setup/config evsel attrs following code is used:
>
> util/evsel.c::perf_evsel__config()
>
> /*
> * We default some events to a 1 default interval. But keep
> * it a weak assumption overridable by the user.
> */
> if (!attr->sample_period || (opts->user_freq != UINT_MAX &&
> opts->user_interval != ULLONG_MAX)) {
> if (opts->freq) {
> perf_evsel__set_sample_bit(evsel, PERIOD);
> attr->freq = 1;
> attr->sample_freq = opts->freq;
> } else {
> attr->sample_period = opts->default_interval;
> }
> }

yes, I think thats right.. we should use || instead of &&

It will allow to change period for event types with predefined
attr->sample_period like tracepoints.

However, I tried with tracepoints and even with this fix
and following command line:

# perf record -e syscalls:sys_enter_read -c 2 ls

you'll still get samples with period 1. The reason is in
kernel code:

static void perf_swevent_event(struct perf_event *event, u64 nr,
struct perf_sample_data *data,
struct pt_regs *regs)
{
...
if ((event->attr.sample_type & PERF_SAMPLE_PERIOD) && !event->attr.freq) {
data->period = nr;
return perf_swevent_overflow(event, 1, data, regs);

bacause above condition is true for tracepoints.

It looks like a bug, but I'm not sure how handy it'd be
set period other than 1 for tracepoints thought.. ;)

Maybe it's not that big issue in comparison of screwing
up other software events processing.

I haven't checked other software events.

jirka


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