linux-kernel - Re: [PATCH V2 1/5] perf/core: Add PERF_SAMPLE_WEIGHT

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Date:   Wed, 27 Jan 2021 20:03:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...nel.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, namhyung@...nel.org, jolsa@...hat.com,
        ak@...ux.intel.com, yao.jin@...ux.intel.com, mpe@...erman.id.au,
        maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH V2 1/5] perf/core: Add PERF_SAMPLE_WEIGHT_STRUCT

On Wed, Jan 27, 2021 at 07:38:41AM -0800, kan.liang@...ux.intel.com wrote:
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index b15e344..13b4019 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -145,12 +145,14 @@ enum perf_event_sample_format {
>  	PERF_SAMPLE_CGROUP			= 1U << 21,
>  	PERF_SAMPLE_DATA_PAGE_SIZE		= 1U << 22,
>  	PERF_SAMPLE_CODE_PAGE_SIZE		= 1U << 23,
> +	PERF_SAMPLE_WEIGHT_STRUCT		= 1U << 24,
>  
> -	PERF_SAMPLE_MAX = 1U << 24,		/* non-ABI */
> +	PERF_SAMPLE_MAX = 1U << 25,		/* non-ABI */
>  
>  	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
>  };
>  
> +#define PERF_SAMPLE_WEIGHT_TYPE	(PERF_SAMPLE_WEIGHT | PERF_SAMPLE_WEIGHT_STRUCT)
>  /*
>   * values to program into branch_sample_type when PERF_SAMPLE_BRANCH is set
>   *
> @@ -890,7 +892,16 @@ enum perf_event_type {
>  	 * 	  char			data[size];
>  	 * 	  u64			dyn_size; } && PERF_SAMPLE_STACK_USER
>  	 *
> -	 *	{ u64			weight;   } && PERF_SAMPLE_WEIGHT
> +	 *	{ union perf_sample_weight
> +	 *	 {
> +	 *		u64		full; && PERF_SAMPLE_WEIGHT
> +	 *		struct {
> +	 *			u32	low_dword;
> +	 *			u16	high_word;
> +	 *			u16	higher_word;
> +	 *		} && PERF_SAMPLE_WEIGHT_STRUCT
> +	 *	 }
> +	 *	}
>  	 *	{ u64			data_src; } && PERF_SAMPLE_DATA_SRC
>  	 *	{ u64			transaction; } && PERF_SAMPLE_TRANSACTION
>  	 *	{ u64			abi; # enum perf_sample_regs_abi
> @@ -1248,4 +1259,13 @@ struct perf_branch_entry {
>  		reserved:40;
>  };
>  
> +union perf_sample_weight {
> +	__u64		full;
> +	struct {
> +		__u32	low_dword;
> +		__u16	high_word;
> +		__u16	higher_word;
> +	};
> +};

*urgh*, my naming lives ... anybody got a better suggestion?

Also, do we want to care about byte order?