Re: [PATCH V3 14/14] coresight: etm-perf: Add support for trace buffer format

[Mike Leach]

On Wed, 27 Jan 2021 at 08:56, Anshuman Khandual
<anshuman.khandual@xxxxxxx> wrote:
>
> From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>
> 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 the TRBE sink driver.
>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 2 ++
>  include/uapi/linux/perf_event.h              | 4 ++++
>  2 files changed, 6 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 1464d8b..7c0e691 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -511,6 +511,7 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
>         if (cpudata->mode != CS_MODE_PERF)
>                 return -EINVAL;
>
> +       perf_aux_output_flag(handle, PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW);
>         /*
>          * If the TRBE was disabled due to lack of space in the AUX buffer or a
>          * spurious fault, the driver leaves it disabled, truncating the buffer.
> @@ -606,6 +607,7 @@ static void trbe_handle_overflow(struct perf_output_handle *handle)
>         size = offset - PERF_IDX2OFF(handle->head, buf);
>         if (buf->snapshot)
>                 handle->head = offset;
> +       perf_aux_output_flag(handle, PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW);
>         perf_aux_output_end(handle, size);
>
>         event_data = perf_aux_output_begin(handle, event);
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 9a5ca45..169e6b3 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -1111,6 +1111,10 @@ 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 */
> +
>  #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 */
> --
> 2.7.4
>

Reviewed-by: Mike Leach <mike.leach@xxxxxxxxxx>
-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK