Re: [PATCH v2 07/10] coresight: trbe: Do not truncate buffer on IRQ
From: Mike Leach <hidden>
Date: 2021-07-26 12:34:53
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Hi Suzuki, On Fri, 23 Jul 2021 at 13:46, Suzuki K Poulose [off-list ref] 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
quoted hunk ↗ jump to hunk
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> --- 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel