[PATCH 3/5] coresight: perf: Don't set the truncated flag in snapshot mode

From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: linux-arm-kernel@lists.infradead.org
Cc: corbet@lwn.net, alexander.shishkin@linux.intel.com,
	coresight@lists.linaro.org, suzuki.poulose@arm.com,
	acme@kernel.org, peterz@infradead.org, mingo@redhat.com,
	mike.leach@arm.com, leo.yan@linaro.org
Subject: [PATCH 3/5] coresight: perf: Don't set the truncated flag in snapshot mode
Date: Wed,  1 May 2019 11:50:50 -0600	[thread overview]
Message-ID: <20190501175052.29667-4-mathieu.poirier@linaro.org> (raw)
In-Reply-To: <20190501175052.29667-1-mathieu.poirier@linaro.org>

This patch avoids setting the truncated flag when operaring in snapshot
mode since the trace buffer is expected to be truncated and discontinuous
from one snapshot to another.  Moreover when the truncated flag is set
the perf core stops enabling the event, waiting for user space to consume
the data.  In snapshot mode this is clearly not what we want since it
results in stale data.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
---
 drivers/hwtracing/coresight/coresight-etb10.c   | 8 +++++++-
 drivers/hwtracing/coresight/coresight-tmc-etf.c | 8 +++++++-
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 8 +++++++-
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
index 0764647b92bc..6ff48be91f61 100644
--- a/drivers/hwtracing/coresight/coresight-etb10.c
+++ b/drivers/hwtracing/coresight/coresight-etb10.c
@@ -535,7 +535,13 @@ static unsigned long etb_update_buffer(struct coresight_device *csdev,
 		lost = true;
 	}
 
-	if (lost)
+	/*
+	 * Don't set the TRUNCATED flag in snapshot mode because 1) the
+	 * captured buffer is expected to be truncated and 2) a full buffer
+	 * prevents the event from being re-enabled by the perf core,
+	 * resulting in stale data being send to user space.
+	 */
+	if (!buf->snapshot && lost)
 		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
 
 	/* finally tell HW where we want to start reading from */
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
index d3025634f5e6..8039bd389034 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -538,7 +538,13 @@ static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
 		lost = true;
 	}
 
-	if (lost)
+	/*
+	 * Don't set the TRUNCATED flag in snapshot mode because 1) the
+	 * captured buffer is expected to be truncated and 2) a full buffer
+	 * prevents the event from being re-enabled by the perf core,
+	 * resulting in stale data being send to user space.
+	 */
+	if (!buf->snapshot && lost)
 		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
 
 	cur = buf->cur;
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index b9881d6d41ba..718586a083af 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1516,7 +1516,13 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
 
 	lost |= etr_buf->full;
 out:
-	if (lost)
+	/*
+	 * Don't set the TRUNCATED flag in snapshot mode because 1) the
+	 * captured buffer is expected to be truncated and 2) a full buffer
+	 * prevents the event from being re-enabled by the perf core,
+	 * resulting in stale data being send to user space.
+	 */
+	if (!etr_perf->snapshot && lost)
 		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
 	return size;
 }
-- 
2.17.1


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