Messages in this thread |  | | From | Mike Leach <> | Date | Mon, 26 Jul 2021 13:34:37 +0100 | Subject | Re: [PATCH v2 07/10] coresight: trbe: Do not truncate buffer on IRQ |
| |
Hi Suzuki,
On Fri, 23 Jul 2021 at 13:46, Suzuki K Poulose <suzuki.poulose@arm.com> 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@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> > --- > 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 >
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
|  |