linux-kernel - Re: [PATCH v2 1/4] perf: Allow using AUX data in perf samples

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Date:   Thu, 24 Oct 2019 16:09:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        jolsa@...hat.com, adrian.hunter@...el.com,
        mathieu.poirier@...aro.org, mark.rutland@....com
Subject: Re: [PATCH v2 1/4] perf: Allow using AUX data in perf samples

On Tue, Oct 22, 2019 at 12:58:09PM +0300, Alexander Shishkin wrote:
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index bb7b271397a6..84dbd1499a24 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -141,8 +141,9 @@ enum perf_event_sample_format {
>  	PERF_SAMPLE_TRANSACTION			= 1U << 17,
>  	PERF_SAMPLE_REGS_INTR			= 1U << 18,
>  	PERF_SAMPLE_PHYS_ADDR			= 1U << 19,
> +	PERF_SAMPLE_AUX				= 1U << 20,
>  
> -	PERF_SAMPLE_MAX = 1U << 20,		/* non-ABI */
> +	PERF_SAMPLE_MAX = 1U << 21,		/* non-ABI */
>  
>  	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
>  };
> @@ -424,7 +425,7 @@ struct perf_event_attr {
>  	 */
>  	__u32	aux_watermark;
>  	__u16	sample_max_stack;
> -	__u16	__reserved_2;	/* align to __u64 */
> +	__u16	aux_sample_size;
>  };

While I understand; would it not be better to make that a u32 (like
sample_stack_user) ? That way we only have to ref the output format and
not also the config format to get more output.

>  /*
> @@ -864,6 +865,8 @@ enum perf_event_type {
>  	 *	{ u64			abi; # enum perf_sample_regs_abi
>  	 *	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
>  	 *	{ u64			phys_addr;} && PERF_SAMPLE_PHYS_ADDR
> +	 *	{ u64			size;
> +	 *	  char			data[size]; } && PERF_SAMPLE_AUX
>  	 * };
>  	 */
>  	PERF_RECORD_SAMPLE			= 9,