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Allocate a byte for advertising the PMU specific format type of the given AUX record. A PMU could end up providing hardware trace data in multiple format in a single session. e.g, The format of hardware buffer produced by CoreSight ETM PMU depends on the type of the "sink" device used for collection for an event (Traditional TMC-ETR/Bs with formatting or TRBEs without any formatting). # Boring story of why this is needed. Goto The_End_of_Story for skipping. CoreSight ETM trace allows instruction level tracing of Arm CPUs. The ETM generates the CPU excecution trace and pumps it into CoreSight AMBA Trace Bus and is collected by a different CoreSight component (traditionally CoreSight TMC-ETR /ETB/ETF), called "sink". Important to note that there is no guarantee that every CPU has a dedicated sink. Thus multiple ETMs could pump the trace data into the same "sink" and thus they apply additional formatting of the trace data for the user to decode it properly and attribute the trace data to the corresponding ETM. However, with the introduction of Arm Trace buffer Extensions (TRBE), we now have a dedicated per-CPU architected sink for collecting the trace. Since the TRBE is always per-CPU, it doesn't apply any formatting of the trace. The support for this driver is under review [1]. Now a system could have a per-cpu TRBE and one or more shared TMC-ETRs on the system. A user could choose a "specific" sink for a perf session (e.g, a TMC-ETR) or the driver could automatically select the nearest sink for a given ETM. It is possible that some ETMs could end up using TMC-ETR (e.g, if the TRBE is not usable on the CPU) while the others using TRBE in a single perf session. Thus we now have "formatted" trace collected from TMC-ETR and "unformatted" trace collected from TRBE. However, we don't get into a situation where a single event could end up using TMC-ETR & TRBE. i.e, any AUX buffer is guaranteed to be either RAW or FORMATTED, but not a mix of both. As for perf decoding, we need to know the type of the data in the individual AUX buffers, so that it can set up the "OpenCSD" (library for decoding CoreSight trace) decoder instance appropriately. Thus the perf.data file must conatin the hints for the tool to decode the data correctly. Since this is a runtime variable, and perf tool doesn't have a control on what sink gets used (in case of automatic sink selection), we need this information made available from the PMU driver for each AUX record. # The_End_of_Story Cc: Peter Ziljstra <peterz@infradead.org> Cc: alexander.shishkin@linux.intel.com Cc: mingo@redhat.com Cc: will@kernel.org Cc: mark.rutland@arm.com Cc: mike.leach@linaro.org Cc: acme@kernel.org Cc: jolsa@redhat.com Cc: Mathieu Poirier <mathieu.poirer@linaro.org> Reviewed by: Mike Leach <mike.leach@linaro.org> Acked-by: Peter Ziljstra <peterz@infradead.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Link: https://lore.kernel.org/r/20210405164307.1720226-2-suzuki.poulose@arm.com Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org> |
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