linux-kernel - [RFC PATCH] perf: Handle multiple formatted AUX records

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Date:   Fri, 22 Jan 2021 15:18:29 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
        Ingo Molnar <mingo@...hat.com>, will@...nel.org,
        mark.rutland@....com, mike.leach@...aro.org, al.grant@....com,
        anshuman.khandual@....com, mathieu.poirier@...aro.org,
        linux-arm-kernel@...ts.infradead.org, jolsa@...hat.com,
        acme@...nel.org, Suzuki K Poulose <suzuki.poulose@....com>
Subject: [RFC PATCH] perf: Handle multiple formatted AUX records

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.

This patch adds a new flag to indicate the trace format
for the given record. Also, includes the changes that
demonstrates how this can be used in the CoreSight PMU
to solve the problem.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 drivers/hwtracing/coresight/coresight-etm-perf.c | 2 ++
 include/linux/coresight.h                        | 1 +
 include/uapi/linux/perf_event.h                  | 1 +
 3 files changed, 4 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index e776a07b0852..81602bd8da59 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -429,6 +429,8 @@ static void etm_event_stop(struct perf_event *event, int mode)

 		size = sink_ops(sink)->update_buffer(sink, handle,
 					      event_data->snk_config);
+		if (!sink->formatted_trace)
+			perf_aux_output_flag(handle, PERF_AUX_FLAG_ALT_FMT);
 		perf_aux_output_end(handle, size);
 	}

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index e019182521a1..45c173c391a4 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -241,6 +241,7 @@ struct coresight_device {
 	int nr_links;
 	bool has_conns_grp;
 	bool ect_enabled; /* true only if associated ect device is enabled */
+	bool formatted_trace; /* Trace is CoreSight formatted ? */
 };

 /*
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index b15e3447cd9f..ea7dcc7b30f0 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1109,6 +1109,7 @@ enum perf_callchain_context {
 #define PERF_AUX_FLAG_OVERWRITE		0x02	/* snapshot from overwrite mode */
 #define PERF_AUX_FLAG_PARTIAL		0x04	/* record contains gaps */
 #define PERF_AUX_FLAG_COLLISION		0x08	/* sample collided with another */
+#define PERF_AUX_FLAG_ALT_FMT		0x10	/* this record is in alternate trace format */

 #define PERF_FLAG_FD_NO_GROUP		(1UL << 0)
 #define PERF_FLAG_FD_OUTPUT		(1UL << 1)
-- 
2.24.1