linux-kernel - Re: [PATCH v5 04/19] perf: aux: Add CoreSight PMU buffer formats

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Message-ID: <YH01bIpu5MSwyqPt@hirez.programming.kicks-ass.net>
Date:   Mon, 19 Apr 2021 09:46:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, mike.leach@...aro.org,
        leo.yan@...aro.org, anshuman.khandual@....com, maz@...nel.org,
        catalin.marinas@....com
Subject: Re: [PATCH v5 04/19] perf: aux: Add CoreSight PMU buffer formats

On Mon, Mar 29, 2021 at 10:56:25AM -0600, Mathieu Poirier wrote:
> Hi Peter,
> 
> On Tue, Mar 23, 2021 at 12:06:32PM +0000, Suzuki K Poulose wrote:
> > CoreSight PMU supports aux-buffer for the ETM tracing. The trace
> > generated by the ETM (associated with individual CPUs, like Intel PT)
> > is captured by a separate IP (CoreSight TMC-ETR/ETF until now).
> > 
> > The TMC-ETR applies formatting of the raw ETM trace data, as it
> > can collect traces from multiple ETMs, with the TraceID to indicate
> > the source of a given trace packet.
> > 
> > Arm Trace Buffer Extension is new "sink" IP, attached to individual
> > CPUs and thus do not provide additional formatting, like TMC-ETR.
> > 
> > Additionally, a system could have both TRBE *and* TMC-ETR for
> > the trace collection. e.g, TMC-ETR could be used as a single
> > trace buffer to collect data from multiple ETMs to correlate
> > the traces from different CPUs. It is possible to have a
> > perf session where some events end up collecting the trace
> > in TMC-ETR while the others in TRBE. Thus we need a way
> > to identify the type of the trace for each AUX record.
> > 
> > Define the trace formats exported by the CoreSight PMU.
> > We don't define the flags following the "ETM" as this
> > information is available to the user when issuing
> > the session. What is missing is the additional
> > formatting applied by the "sink" which is decided
> > at the runtime and the user may not have a control on.
> > 
> > So we define :
> >  - CORESIGHT format (indicates the Frame format)
> >  - RAW format (indicates the format of the source)
> > 
> > The default value is CORESIGHT format for all the records
> > (i,e == 0). Add the RAW format for others that use
> > raw format.
> > 
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Mike Leach <mike.leach@...aro.org>
> > Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> > Cc: Leo Yan <leo.yan@...aro.org>
> > Cc: Anshuman Khandual <anshuman.khandual@....com>
> > Reviewed-by: Mike Leach <mike.leach@...aro.org>
> > Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> > ---
> >  include/uapi/linux/perf_event.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index f006eeab6f0e..63971eaef127 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -1162,6 +1162,10 @@ enum perf_callchain_context {
> >  #define PERF_AUX_FLAG_COLLISION			0x08	/* sample collided with another */
> >  #define PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK	0xff00	/* PMU specific trace format type */
> >  
> > +/* CoreSight PMU AUX buffer formats */
> > +#define PERF_AUX_FLAG_CORESIGHT_FORMAT_CORESIGHT	0x0000 /* Default for backward compatibility */
> > +#define PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW		0x0100 /* Raw format of the source */
> > +
> 
> Have you had time to review this patch?  Anything you'd like to see modified?

Ok I suppose..

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>