linux-kernel - Re: [PATCH v2 1/5] perf/core: add PERF_RECORD_SAMPLE_SKID

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Message-ID: <CABPqkBSi0fOc0pg7SXMSe46aG0T9c9JHfriv3vCaKm30fOi5qA@mail.gmail.com>
Date:   Thu, 2 Nov 2017 12:46:35 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>, mingo@...e.hu,
        ak@...ux.intel.com, "Liang, Kan" <kan.liang@...el.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Stephane Eranian <eranian@...il.com>
Subject: Re: [PATCH v2 1/5] perf/core: add PERF_RECORD_SAMPLE_SKID_IP record type

On Thu, Nov 2, 2017 at 11:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Nov 02, 2017 at 11:15:55AM -0700, Stephane Eranian wrote:
>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index 874b71a70058..772530501025 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -917,6 +917,7 @@ struct perf_sample_data {
>>       u64                             stack_user_size;
>>
>>       u64                             phys_addr;
>> +     u64                             skid_ip;
>>  } ____cacheline_aligned;
>>
>>  /* default value for data source */
>> @@ -937,6 +938,7 @@ static inline void perf_sample_data_init(struct perf_sample_data *data,
>>       data->weight = 0;
>>       data->data_src.val = PERF_MEM_NA;
>>       data->txn = 0;
>> +     data->skid_ip = 0; /* mark as uinitialized */
>>  }
>
> I keep forgetting to write the comment explaining how this function only
> touches a single cacheline; you just wrecked that :/

Ok, but I need to add that field. So are you saying there is a pad I
could use instead?