Re: [PATCH v2 00/10] coresight: TRBE and Self-Hosted trace fixes
From: Suzuki K Poulose
Date: Fri Jul 23 2021 - 09:45:50 EST
On 23/07/2021 13:46, Suzuki K Poulose wrote:
This series fixes the following issues with the TRBE and Self-Hosted
trace for CoreSight.
The Self-hosted trace filter control registers are now save-restored
across CPU PM event. And more importantly the Trace Filtering is now
used to control per ETM session (rather than allowing the trace
throughout the life time of the system). i.e, ETM configuration of
the given run is used to enforce trace filtering (TRFCR) along with the
Trace Exclusion controls in TRCVICTLR.
For the TRBE, we were using the TRUNCATED flag in the AUX buffer on
every IRQ to indicate that we may have lost a few bytes of trace. But
this causes the event to be disabled until the userspace re-enables
it back, even when there is space left in the ring buffer. To make
things worse, we were restarting the AUX handle, which would soon
be disabled, potentially creating 0 sized records (without truncation),
which the perf tool tends to ignore. This might cause the event to be
disabled permanently. Also, sometimes we leave the buffer TRUNCATED,
but delay the closing of the handle to event schedule out, which could
cause significant black out in the trace capture. This was reported
by Tamas Zsoldos.
This series removes the use of TRUNCATED flag for every IRQ. Instead,
it is only used if we really run out of space in the buffer. And also
we make sure the "handle" is closed immediately on TRUNCATED case,
which triggers the userspace to take action. The core perf layer has
been hardened to handle this case where a "handle" is closed out.
Finally, we make sure that the CPU trace is prohibited, when the TRBE
is left disabled. The ETE/ETM driver will program the Trace Filtering
appropriately since we do this dynamically now with the first half
of the series.
The series is also available here :
https://git.gitlab.arm.com/linux-arm/linux-skp.git
coresight/trbe-self-hosted-fixes/v2
Suzuki