From: "Liang, Kan" <kan.liang@intel.com>
To: Stephane Eranian <eranian@google.com>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "acme@redhat.com" <acme@redhat.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "mingo@elte.hu" <mingo@elte.hu>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "jolsa@redhat.com" <jolsa@redhat.com>
Subject: RE: [PATCH 2/5] perf/x86: add PERF_SAMPLE_SKID_IP support for X86
 PEBS
Thread-Topic: [PATCH 2/5] perf/x86: add PERF_SAMPLE_SKID_IP support for X86
 PEBS
Thread-Index: AQHS5d9QkR1P9EpkpkGksCWnOcBxc6ImDj8A//+L2ACAAI0YAA==
Date: Thu, 15 Jun 2017 17:18:39 +0000
Message-ID: <37D7C6CF3E00A74B8858931C1DB2F0775370DD61@SHSMSX103.ccr.corp.intel.com>
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> 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
> >