linux-kernel - Re: [PATCH 2/5] perf/x86: add PERF_SAMPLE_SKID

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Date:   Thu, 15 Jun 2017 09:39:36 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "acme@...hat.com" <acme@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...e.hu" <mingo@...e.hu>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>
Subject: Re: [PATCH 2/5] perf/x86: add PERF_SAMPLE_SKID_IP support for X86 PEBS

On Thu, Jun 15, 2017 at 8:40 AM, Liang, Kan <kan.liang@...el.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.

> Thanks,
> Kan
>
>>
>> Signed-off-by: Stephane Eranian <eranian@...gle.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
>