linux-kernel - Re: [PATCH 01/10] perf/core, x86: Add PERF_SAMPLE_LBR

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Message-ID: <20191008083141.GH2294@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Oct 2019 10:31:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...nel.org, linux-kernel@...r.kernel.org,
        jolsa@...nel.org, namhyung@...nel.org, ak@...ux.intel.com,
        vitaly.slobodskoy@...el.com, pavel.gerasimov@...el.com
Subject: Re: [PATCH 01/10] perf/core, x86: Add PERF_SAMPLE_LBR_TOS

On Mon, Oct 07, 2019 at 10:59:01AM -0700, kan.liang@...ux.intel.com wrote:
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 61448c19a132..ee9ef0c4cb08 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -100,6 +100,7 @@ struct perf_raw_record {
>   */
>  struct perf_branch_stack {
>  	__u64				nr;
> +	__u64				tos;
>  	struct perf_branch_entry	entries[0];
>  };
>  
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index bb7b271397a6..fe36ebb7dc2e 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_LBR_TOS			= 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 */
>  };
> @@ -864,6 +865,7 @@ 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			tos;} && PERF_SAMPLE_LBR_TOS
>  	 * };
>  	 */
>  	PERF_RECORD_SAMPLE			= 9,

I have problems with the API.. You're introducing the intel specific LBR
naming, and adding a whole new sample type vs extending the existing
BRANCH_STACK (like you really already do with struct perf_branch_stack).

So why not add a bit to PERF_SAMPLE_BRANCH_* to request the presence of
the TOS field in the PERF_SAMPLE_BRANCH_STACK output?