Messages in this thread |  | | Date | Fri, 5 Dec 2025 09:58:02 +0530 | | Subject | Re: [PATCH 08/19] coresight: trbe: Use PERF_AUX_FLAG_PARTIAL instead of PERF_AUX_FLAG_COLLISION | | From | Anshuman Khandual <> |
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On 01/12/25 4:51 PM, Leo Yan wrote: > When tracing stops, there is no collision with other samples, so using > PERF_AUX_FLAG_COLLISION does not accurately reflect the trace state and > may mislead userspace. > > Use PERF_AUX_FLAG_PARTIAL instead to indicate that tracing stopped and > the record may contain gaps. > > Signed-off-by: Leo Yan <leo.yan@arm.com> > --- > drivers/hwtracing/coresight/coresight-trbe.c | 19 ++++++------------- > 1 file changed, 6 insertions(+), 13 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c > index b06885a08e082fd34f68d9588518807b5c47c86e..0caa4a6b437a3aa39fc6bcc72a23711b54f7c598 100644 > --- a/drivers/hwtracing/coresight/coresight-trbe.c > +++ b/drivers/hwtracing/coresight/coresight-trbe.c > @@ -669,21 +669,14 @@ static enum trbe_fault_action trbe_get_fault_act(struct perf_output_handle *hand > } > > /* > - * 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. > + * Mark the buffer to indicate that the trace is stopped by setting > + * the PARTIAL 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 > + * TRBE event was detected and the IRQ was consumed by the CPU. > */ > if (!is_trbe_running(trbsr)) > - perf_aux_output_flag(handle, PERF_AUX_FLAG_COLLISION); > + perf_aux_output_flag(handle, PERF_AUX_FLAG_PARTIAL);
This is interesting. So there is a no possibility for the records to be overridden in the perf ring buffer and incomplete record is all that can happen when TRBE is stopped, without stopping the ETE first ? Could both of these scenarios might be possible as well ?
> > if (is_trbe_wrap(trbsr)) > return TRBE_FAULT_ACT_WRAP; >
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