Hi Suzuki,
On Fri, 23 Jul 2021 at 13:46, Suzuki K Poulose <suzuki.poulose@xxxxxxx> 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.
What is the user visible behaviour when using COLLISION?
The TRUNCATE warning is at least accurate - even if the KVM thing is
something of a red herring.
It is easier to explain a "scary" warning, than try to debug someones
problems if perf is silent or misleading when using the COLLISION
flag.
Regards
Mike
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@xxxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxx>
Cc: Mike Leach <mike.leach@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Leo Yan <leo.yan@xxxxxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
---
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 503bea0137ae..d50f142e86d1 100644
--- a/drivers/hwtracing/coresight/coresight-trbe.c
+++ b/drivers/hwtracing/coresight/coresight-trbe.c
@@ -615,7 +615,7 @@ 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;
@@ -708,7 +708,7 @@ static void trbe_handle_overflow(struct perf_output_handle *handle)
* collection upon the WRAP event, without stopping the source.
*/
perf_aux_output_flag(handle, PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW |
- PERF_AUX_FLAG_TRUNCATED);
+ PERF_AUX_FLAG_COLLISION);
perf_aux_output_end(handle, size);
event_data = perf_aux_output_begin(handle, event);
if (!event_data) {
--
2.24.1