linux-kernel - Re: [RFC 02/11] perf/core: Data structure to present hazard data

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Date:   Mon, 2 Mar 2020 14:48:43 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, peterz@...radead.org, mpe@...erman.id.au,
        paulus@...ba.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, adrian.hunter@...el.com, ak@...ux.intel.com,
        kan.liang@...ux.intel.com, alexey.budankov@...ux.intel.com,
        yao.jin@...ux.intel.com, robert.richter@....com,
        kim.phillips@....com, maddy@...ux.ibm.com,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Subject: Re: [RFC 02/11] perf/core: Data structure to present hazard data

On Mon, Mar 02, 2020 at 10:53:46AM +0530, Ravi Bangoria wrote:
> From: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
> 
> Introduce new perf sample_type PERF_SAMPLE_PIPELINE_HAZ to request kernel
> to provide cpu pipeline hazard data. Also, introduce arch independent
> structure 'perf_pipeline_haz_data' to pass hazard data to userspace. This
> is generic structure and arch specific data needs to be converted to this
> format.
> 
> Signed-off-by: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> ---
>  include/linux/perf_event.h            |  7 ++++++
>  include/uapi/linux/perf_event.h       | 32 ++++++++++++++++++++++++++-
>  kernel/events/core.c                  |  6 +++++
>  tools/include/uapi/linux/perf_event.h | 32 ++++++++++++++++++++++++++-
>  4 files changed, 75 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 547773f5894e..d5b606e3c57d 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1001,6 +1001,7 @@ struct perf_sample_data {
>  	u64				stack_user_size;
>  
>  	u64				phys_addr;
> +	struct perf_pipeline_haz_data	pipeline_haz;
>  } ____cacheline_aligned;
>  
>  /* default value for data source */
> @@ -1021,6 +1022,12 @@ 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->pipeline_haz.itype = PERF_HAZ__ITYPE_NA;
> +	data->pipeline_haz.icache = PERF_HAZ__ICACHE_NA;
> +	data->pipeline_haz.hazard_stage = PERF_HAZ__PIPE_STAGE_NA;
> +	data->pipeline_haz.hazard_reason = PERF_HAZ__HREASON_NA;
> +	data->pipeline_haz.stall_stage = PERF_HAZ__PIPE_STAGE_NA;
> +	data->pipeline_haz.stall_reason = PERF_HAZ__SREASON_NA;
>  }
>  
>  extern void perf_output_sample(struct perf_output_handle *handle,
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 377d794d3105..ff252618ca93 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -142,8 +142,9 @@ enum perf_event_sample_format {
>  	PERF_SAMPLE_REGS_INTR			= 1U << 18,
>  	PERF_SAMPLE_PHYS_ADDR			= 1U << 19,
>  	PERF_SAMPLE_AUX				= 1U << 20,
> +	PERF_SAMPLE_PIPELINE_HAZ		= 1U << 21,

Can we please have perf_event_open() reject this sample flag for PMUs
without the new callback (introduced in the next patch)?

That way it'll be possible to detect whether the PMU exposes this.

Thanks,
Mark.