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authorSuzuki K Poulose <suzuki.poulose@arm.com>2021-09-23 17:39:17 +0300
committerMathieu Poirier <mathieu.poirier@linaro.org>2021-10-27 20:45:30 +0300
commit0a5f355633eaacb7300598d96e8013a401a02c5e (patch)
treea8b55619f036a423768953829bb440d77c6cfa5e /drivers/hwtracing
parent7037a39d379733f5352af5e04a202dad35562ef3 (diff)
downloadlinux-0a5f355633eaacb7300598d96e8013a401a02c5e.tar.xz
coresight: trbe: Do not truncate buffer on IRQ
The TRBE driver marks the AUX buffer as TRUNCATED when we get an IRQ on FILL event. This has rather unwanted side-effect of the event being disabled when there may be more space in the ring buffer. So, instead of TRUNCATE we need a different flag to indicate that the trace may have lost a few bytes (i.e from the point of generating the FILL event until the IRQ is consumed). Anyways, the userspace must use the size from RECORD_AUX headers to restrict the "trace" decoding. Using PARTIAL flag causes the perf tool to generate the following warning: Warning: AUX data had gaps in it XX times out of YY! Are you running a KVM guest in the background? which is pointlessly scary for a user. The other remaining options are : - COLLISION - Use by SPE to indicate samples collided - Add a new flag - Specifically for CoreSight, doesn't sound so good, if we can re-use something. Given that we don't already use the "COLLISION" flag, the above behavior can be notified using this flag for CoreSight. Cc: Mathieu Poirier <mathieu.poirier@linaro.org> Cc: James Clark <james.clark@arm.com> Cc: Mike Leach <mike.leach@linaro.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Leo Yan <leo.yan@linaro.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Link: https://lore.kernel.org/r/20210923143919.2944311-4-suzuki.poulose@arm.com Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Diffstat (limited to 'drivers/hwtracing')
-rw-r--r--drivers/hwtracing/coresight/coresight-trbe.c27
1 files changed, 21 insertions, 6 deletions
diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
index 47120d263639..0a9106c15639 100644
--- a/drivers/hwtracing/coresight/coresight-trbe.c
+++ b/drivers/hwtracing/coresight/coresight-trbe.c
@@ -120,6 +120,25 @@ static void trbe_reset_local(void)
write_sysreg_s(0, SYS_TRBSR_EL1);
}
+static void trbe_report_wrap_event(struct perf_output_handle *handle)
+{
+ /*
+ * Mark the buffer to indicate that there was a WRAP event by
+ * setting the COLLISION flag. This indicates to the user that
+ * the TRBE trace collection was stopped without stopping the
+ * ETE and thus there might be some amount of trace that was
+ * lost between the time the WRAP was detected and the IRQ
+ * was consumed by the CPU.
+ *
+ * Setting the TRUNCATED flag would move the event to STOPPED
+ * state unnecessarily, even when there is space left in the
+ * ring buffer. Using the COLLISION flag doesn't have this side
+ * effect. We only set TRUNCATED flag when there is no space
+ * left in the ring buffer.
+ */
+ perf_aux_output_flag(handle, PERF_AUX_FLAG_COLLISION);
+}
+
static void trbe_stop_and_truncate_event(struct perf_output_handle *handle)
{
struct trbe_buf *buf = etm_perf_sink_config(handle);
@@ -612,7 +631,7 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
* for correct size. Also, mark the buffer truncated.
*/
write = get_trbe_limit_pointer();
- perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
+ trbe_report_wrap_event(handle);
}
offset = write - base;
@@ -708,11 +727,7 @@ static void trbe_handle_overflow(struct perf_output_handle *handle)
if (buf->snapshot)
handle->head += size;
- /*
- * Mark the buffer as truncated, as we have stopped the trace
- * collection upon the WRAP event, without stopping the source.
- */
- perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
+ trbe_report_wrap_event(handle);
perf_aux_output_end(handle, size);
event_data = perf_aux_output_begin(handle, event);
if (!event_data) {