On Wed, 27 Jan 2021 at 08:56, Anshuman Khandual <[email protected]> wrote: > > From: Suzuki K Poulose <[email protected]> > > 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 <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: Mathieu Poirier <[email protected]> > Signed-off-by: Suzuki K Poulose <[email protected]> > Signed-off-by: Anshuman Khandual <[email protected]> > --- > include/uapi/linux/perf_event.h | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index b15e344..9a5ca45 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -1105,10 +1105,11 @@ enum perf_callchain_context { > /** > * PERF_RECORD_AUX::flags bits > */ > -#define PERF_AUX_FLAG_TRUNCATED 0x01 /* record was > truncated to fit */ > -#define PERF_AUX_FLAG_OVERWRITE 0x02 /* snapshot from > overwrite mode */ > -#define PERF_AUX_FLAG_PARTIAL 0x04 /* record contains gaps */ > -#define PERF_AUX_FLAG_COLLISION 0x08 /* sample collided > with another */ > +#define PERF_AUX_FLAG_TRUNCATED 0x01 /* record was > truncated to fit */ > +#define PERF_AUX_FLAG_OVERWRITE 0x02 /* snapshot > from overwrite mode */ > +#define PERF_AUX_FLAG_PARTIAL 0x04 /* record contains > gaps */ > +#define PERF_AUX_FLAG_COLLISION 0x08 /* sample > collided with another */ > +#define PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK 0xff00 /* PMU specific trace > format type */ > > #define PERF_FLAG_FD_NO_GROUP (1UL << 0) > #define PERF_FLAG_FD_OUTPUT (1UL << 1) > -- > 2.7.4 >
Reviewed by: Mike Leach <[email protected]> -- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
