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

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Message-ID: <20171102185939.xxyu6quthqpe5xfh@hirez.programming.kicks-ass.net>
Date:   Thu, 2 Nov 2017 19:59:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     linux-kernel@...r.kernel.org, acme@...hat.com, mingo@...e.hu,
        ak@...ux.intel.com, kan.liang@...el.com, 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 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 :/