Re: [PATCH v2 12/13] coresight: events: PERF_RECORD_AUX_OUTPUT_HW_ID used for Trace ID

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 04/07/2022 09:11, Mike Leach wrote:
> Use the perf_report_aux_output_id() call to output the CoreSight trace ID
> and associated CPU as a PERF_RECORD_AUX_OUTPUT_HW_ID record in the
> perf.data file.
> 
> Signed-off-by: Mike Leach <mike.leach@linaro.org>
> ---
>   drivers/hwtracing/coresight/coresight-etm-perf.c | 10 ++++++++++
>   include/linux/coresight-pmu.h                    | 14 ++++++++++++++
>   2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index ad3fdc07c60b..531f5d42272b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -4,6 +4,7 @@
>    * Author: Mathieu Poirier <mathieu.poirier@linaro.org>
>    */
>   
> +#include <linux/bitfield.h>
>   #include <linux/coresight.h>
>   #include <linux/coresight-pmu.h>
>   #include <linux/cpumask.h>
> @@ -437,6 +438,7 @@ static void etm_event_start(struct perf_event *event, int flags)
>   	struct perf_output_handle *handle = &ctxt->handle;
>   	struct coresight_device *sink, *csdev = per_cpu(csdev_src, cpu);
>   	struct list_head *path;
> +	u64 hw_id;
>   
>   	if (!csdev)
>   		goto fail;
> @@ -482,6 +484,11 @@ static void etm_event_start(struct perf_event *event, int flags)
>   	if (source_ops(csdev)->enable(csdev, event, CS_MODE_PERF))
>   		goto fail_disable_path;
>   
> +	/* output cpu / trace ID in perf record */
> +	hw_id = FIELD_PREP(CS_AUX_HW_ID_VERSION_MASK, CS_AUX_HW_ID_CURR_VERSION) |
> +		FIELD_PREP(CS_AUX_HW_ID_TRACE_ID_MASK, coresight_trace_id_get_cpu_id(cpu));
> +	perf_report_aux_output_id(event, hw_id);
> +
>   out:
>   	/* Tell the perf core the event is alive */
>   	event->hw.state = 0;
> @@ -600,6 +607,9 @@ static void etm_event_stop(struct perf_event *event, int mode)
>   
>   	/* Disabling the path make its elements available to other sessions */
>   	coresight_disable_path(path);
> +
> +	/* release the trace ID we read on event start */
> +	coresight_trace_id_put_cpu_id(cpu);
>   }
>   
>   static int etm_event_add(struct perf_event *event, int mode)
> diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
> index 9f7ee380266b..5572d0e10822 100644
> --- a/include/linux/coresight-pmu.h
> +++ b/include/linux/coresight-pmu.h
> @@ -7,6 +7,8 @@
>   #ifndef _LINUX_CORESIGHT_PMU_H
>   #define _LINUX_CORESIGHT_PMU_H
>   
> +#include <linux/bits.h>
> +
>   #define CORESIGHT_ETM_PMU_NAME "cs_etm"
>   
>   /*
> @@ -38,4 +40,16 @@
>   #define ETM4_CFG_BIT_RETSTK	12
>   #define ETM4_CFG_BIT_VMID_OPT	15
>   
> +/*
> + * Interpretation of the PERF_RECORD_AUX_OUTPUT_HW_ID payload.
> + * Used to associate a CPU with the CoreSight Trace ID.
> + * [63:16] - unused SBZ
> + * [15:08] - Trace ID
> + * [07:00] - Version

Could we please re-arrange the fields, such that it is easier to
comprehend the TraceID looking at the raw trace dump ? Also to
accommodate the future changes.

e.g,
       [15:00] - Trace ID	 /* For future expansion, if at all */
       [59:16] - RES0
       [63:60] - Trace_ID_Version

I think we *might* (not sure yet) end up adding "sinkid" when we have
sink specific allocation, so that we can associate the HW_ID of an event
to the "AUXTRACE" record (i.e., trace buffer).

So if we need to do that we could:

       [15:00] - Trace ID	 /* For future expansion, if at all */
       [47:16] - Trace Pool ID( == 0 if global, == sink_id if sink based)
       [59:48] - RES0
       [63:60] - Trace_ID_Version == 1

Or we could adopt the above straight away.

Thoughts ?

Suzuki

> + */
> +#define CS_AUX_HW_ID_VERSION_MASK	GENMASK_ULL(7, 0)
> +#define CS_AUX_HW_ID_TRACE_ID_MASK	GENMASK_ULL(15, 8)
> +
> +#define CS_AUX_HW_ID_CURR_VERSION 0


> +
>   #endif