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From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: linux-arm-kernel@lists.infradead.org
Cc: suzuki.poulose@arm.com, alexander.shishkin@linux.intel.com,
	coresight@lists.linaro.org, acme@kernel.org,
	peterz@infradead.org, mingo@redhat.com, leo.yan@linaro.org,
	mike.leach@linaro.org
Subject: [PATCH V2 5/6] coresight: perf: Don't set the truncated flag in snapshot mode
Date: Tue, 14 May 2019 13:40:17 -0600	[thread overview]
Message-ID: <20190514194018.23420-6-mathieu.poirier@linaro.org> (raw)
In-Reply-To: <20190514194018.23420-1-mathieu.poirier@linaro.org>

This patch avoids setting the truncated flag when operating 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 60e753b1768d..516d67cd7759 100644
--- a/drivers/hwtracing/coresight/coresight-etb10.c
+++ b/drivers/hwtracing/coresight/coresight-etb10.c
@@ -512,7 +512,13 @@ 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 31d41e2ad955..bd5f3b57eebd 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -518,7 +518,13 @@ 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 cc8401c76c39..1fc3db8045e1 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1511,7 +1511,13 @@ 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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  parent reply	other threads:[~2019-05-14 19:41 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-14 19:40 [PATCH V2 0/6] coresight: Fix snapshot mode Mathieu Poirier
2019-05-14 19:40 ` [PATCH V2 1/6] coresight: etb10: Properly set AUX buffer head in " Mathieu Poirier
2019-05-15  9:45   ` Suzuki K Poulose
2019-05-15 14:28     ` Mathieu Poirier
2019-05-16  9:41       ` Suzuki K Poulose
2019-05-14 19:40 ` [PATCH V2 2/6] coresight: tmc-etr: " Mathieu Poirier
2019-05-14 19:40 ` [PATCH V2 3/6] coresight: tmc-etf: " Mathieu Poirier
2019-05-14 19:40 ` [PATCH V2 4/6] coresight: tmc-etf: Fix snapshot mode update function Mathieu Poirier
2019-05-14 19:40 ` Mathieu Poirier [this message]
2019-05-16 15:22   ` [PATCH V2 5/6] coresight: perf: Don't set the truncated flag in snapshot mode Suzuki K Poulose
2019-05-14 19:40 ` [PATCH V2 6/6] perf tools: Properly set the value of 'old' and 'head' " Mathieu Poirier
2019-05-16 15:00   ` Leo Yan
2019-05-20 19:53     ` Mathieu Poirier
2019-05-21  1:54       ` Leo Yan
2019-05-16 15:09 ` [PATCH V2 0/6] coresight: Fix " Leo Yan

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