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 --- Changes since v2: - The perf tool patch for reporting collisions is queued. --- drivers/hwtracing/coresight/coresight-trbe.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c index de99dd0aecd3..a1a15fa6c4ae 100644 --- a/drivers/hwtracing/coresight/coresight-trbe.c +++ b/drivers/hwtracing/coresight/coresight-trbe.c @@ -612,7 +612,7 @@ 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); + perf_aux_output_flag(handle, PERF_AUX_FLAG_COLLISION); }
offset = write - base; @@ -705,7 +705,7 @@ static void trbe_handle_overflow(struct perf_output_handle *handle) * 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); + perf_aux_output_flag(handle, PERF_AUX_FLAG_COLLISION); perf_aux_output_end(handle, size); event_data = perf_aux_output_begin(handle, event); if (!event_data) {