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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>
This commit is contained in:
Suzuki K Poulose 2021-09-23 15:39:17 +01:00 committed by Mathieu Poirier
parent 7037a39d37
commit 0a5f355633
1 changed files with 21 additions and 6 deletions
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27
drivers/hwtracing/coresight/coresight-trbe.c
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@ -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) {