Re: [PATCH v3 07/10] coresight: trbe: Do not truncate buffer on IRQ
From: Anshuman Khandual <hidden>
Date: 2021-09-15 06:45:43
On 9/14/21 3:56 PM, Suzuki K Poulose wrote:
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 <redacted>
Cc: Mike Leach <redacted>
Cc: Anshuman Khandual <redacted>
Cc: Leo Yan <redacted>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>Reviewed-by: Anshuman Khandual <redacted>
quoted hunk ↗ jump to hunk
--- 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) {
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