linux-kernel - Re: [PATCH v5 04/19] perf: aux: Add CoreSight PMU buffer formats

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Date:   Mon, 29 Mar 2021 10:56:25 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, mike.leach@...aro.org,
        leo.yan@...aro.org, anshuman.khandual@....com, maz@...nel.org,
        catalin.marinas@....com, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 04/19] perf: aux: Add CoreSight PMU buffer formats

Hi Peter,

On Tue, Mar 23, 2021 at 12:06:32PM +0000, Suzuki K Poulose wrote:
> CoreSight PMU supports aux-buffer for the ETM tracing. The trace
> generated by the ETM (associated with individual CPUs, like Intel PT)
> is captured by a separate IP (CoreSight TMC-ETR/ETF until now).
> 
> The TMC-ETR applies formatting of the raw ETM trace data, as it
> can collect traces from multiple ETMs, with the TraceID to indicate
> the source of a given trace packet.
> 
> Arm Trace Buffer Extension is new "sink" IP, attached to individual
> CPUs and thus do not provide additional formatting, like TMC-ETR.
> 
> Additionally, a system could have both TRBE *and* TMC-ETR for
> the trace collection. e.g, TMC-ETR could be used as a single
> trace buffer to collect data from multiple ETMs to correlate
> the traces from different CPUs. It is possible to have a
> perf session where some events end up collecting the trace
> in TMC-ETR while the others in TRBE. Thus we need a way
> to identify the type of the trace for each AUX record.
> 
> Define the trace formats exported by the CoreSight PMU.
> We don't define the flags following the "ETM" as this
> information is available to the user when issuing
> the session. What is missing is the additional
> formatting applied by the "sink" which is decided
> at the runtime and the user may not have a control on.
> 
> So we define :
>  - CORESIGHT format (indicates the Frame format)
>  - RAW format (indicates the format of the source)
> 
> The default value is CORESIGHT format for all the records
> (i,e == 0). Add the RAW format for others that use
> raw format.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Reviewed-by: Mike Leach <mike.leach@...aro.org>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  include/uapi/linux/perf_event.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index f006eeab6f0e..63971eaef127 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -1162,6 +1162,10 @@ enum perf_callchain_context {
>  #define PERF_AUX_FLAG_COLLISION			0x08	/* sample collided with another */
>  #define PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK	0xff00	/* PMU specific trace format type */
>  
> +/* CoreSight PMU AUX buffer formats */
> +#define PERF_AUX_FLAG_CORESIGHT_FORMAT_CORESIGHT	0x0000 /* Default for backward compatibility */
> +#define PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW		0x0100 /* Raw format of the source */
> +

Have you had time to review this patch?  Anything you'd like to see modified?

Thanks,
Mathieu

>  #define PERF_FLAG_FD_NO_GROUP		(1UL << 0)
>  #define PERF_FLAG_FD_OUTPUT		(1UL << 1)
>  #define PERF_FLAG_PID_CGROUP		(1UL << 2) /* pid=cgroup id, per-cpu mode only */
> -- 
> 2.24.1
>