RE: [PATCH 2/5] perf/x86: add PERF_SAMPLE_SKID_IP support for X86 PEBS

Liang, Kan
2017-06-15T17:18:48Z

> On Thu, Jun 15, 2017 at 8:40 AM, Liang, Kan <kan.liang@intel.com> wrote:
> >
> >
> >> This patch adds support for SKID_IP to Intel x86 processors in PEBS
> >> mode. In that case, the off-by-1 IP from PEBS is returned in the SKID_IP
> field.
> >
> > It looks we can only get different skid_ip and ip with :pp event (attr.precise
> = 2).
> > With the :p event (attr.precise = 1), the skid_ip and ip are the same. Right?
> >
> Correct, because skid_ip would be equal to the pebs->ip.

I think it's better to make it clear for user by adding a check in perf tool.
If --skid-ip is applied with :p event/non-PEBS event, the tool may
suggest them to use :pp event instead.

Thanks,
Kan
> >
> >>
> >> Signed-off-by: Stephane Eranian <eranian@google.com>
> >> ---
> >> arch/x86/events/intel/ds.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> >> index c6d23ffe422d..ee17de5d6b8d 100644
> >> --- a/arch/x86/events/intel/ds.c
> >> +++ b/arch/x86/events/intel/ds.c
> >> @@ -1169,6 +1169,13 @@ static void setup_pebs_sample_data(struct
> >> perf_event *event,
> >> x86_pmu.intel_cap.pebs_format >= 1)
> >> data->addr = pebs->dla;
> >>
> >> + /*
> >> + * unmodified, skid IP which is guaranteed to be the next
> >> + * dyanmic instruction
> >> + */
> >> + if (sample_type & PERF_SAMPLE_SKID_IP)
> >> + data->skid_ip = pebs->ip;
> >> +
> >> if (x86_pmu.intel_cap.pebs_format >= 2) {
> >> /* Only set the TSX weight when no memory weight. */
> >> if ((sample_type & PERF_SAMPLE_WEIGHT) && !fll)
> >> --
> >> 2.13.1.518.g3df882009-goog
> >