linux-kernel - Re: [PATCH v2 12/13] coresight: events: PERF_RECORD_AUX_OUTPUT_HW

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Date:   Wed, 20 Jul 2022 11:53:58 +0100
From:   Mike Leach <mike.leach@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-perf-users@...r.kernel.org, leo.yan@...aro.org,
        quic_jinlmao@...cinc.com
Subject: Re: [PATCH v2 12/13] coresight: events: PERF_RECORD_AUX_OUTPUT_HW_ID
 used for Trace ID

Hi Suzuki,

On Wed, 20 Jul 2022 at 10:30, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>
> On 04/07/2022 09:11, Mike Leach wrote:
> > Use the perf_report_aux_output_id() call to output the CoreSight trace ID
> > and associated CPU as a PERF_RECORD_AUX_OUTPUT_HW_ID record in the
> > perf.data file.
> >
> > Signed-off-by: Mike Leach <mike.leach@...aro.org>
> > ---
> >   drivers/hwtracing/coresight/coresight-etm-perf.c | 10 ++++++++++
> >   include/linux/coresight-pmu.h                    | 14 ++++++++++++++
> >   2 files changed, 24 insertions(+)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > index ad3fdc07c60b..531f5d42272b 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > @@ -4,6 +4,7 @@
> >    * Author: Mathieu Poirier <mathieu.poirier@...aro.org>
> >    */
> >
> > +#include <linux/bitfield.h>
> >   #include <linux/coresight.h>
> >   #include <linux/coresight-pmu.h>
> >   #include <linux/cpumask.h>
> > @@ -437,6 +438,7 @@ static void etm_event_start(struct perf_event *event, int flags)
> >       struct perf_output_handle *handle = &ctxt->handle;
> >       struct coresight_device *sink, *csdev = per_cpu(csdev_src, cpu);
> >       struct list_head *path;
> > +     u64 hw_id;
> >
> >       if (!csdev)
> >               goto fail;
> > @@ -482,6 +484,11 @@ static void etm_event_start(struct perf_event *event, int flags)
> >       if (source_ops(csdev)->enable(csdev, event, CS_MODE_PERF))
> >               goto fail_disable_path;
> >
> > +     /* output cpu / trace ID in perf record */
> > +     hw_id = FIELD_PREP(CS_AUX_HW_ID_VERSION_MASK, CS_AUX_HW_ID_CURR_VERSION) |
> > +             FIELD_PREP(CS_AUX_HW_ID_TRACE_ID_MASK, coresight_trace_id_get_cpu_id(cpu));
> > +     perf_report_aux_output_id(event, hw_id);
> > +
> >   out:
> >       /* Tell the perf core the event is alive */
> >       event->hw.state = 0;
> > @@ -600,6 +607,9 @@ static void etm_event_stop(struct perf_event *event, int mode)
> >
> >       /* Disabling the path make its elements available to other sessions */
> >       coresight_disable_path(path);
> > +
> > +     /* release the trace ID we read on event start */
> > +     coresight_trace_id_put_cpu_id(cpu);
> >   }
> >
> >   static int etm_event_add(struct perf_event *event, int mode)
> > diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
> > index 9f7ee380266b..5572d0e10822 100644
> > --- a/include/linux/coresight-pmu.h
> > +++ b/include/linux/coresight-pmu.h
> > @@ -7,6 +7,8 @@
> >   #ifndef _LINUX_CORESIGHT_PMU_H
> >   #define _LINUX_CORESIGHT_PMU_H
> >
> > +#include <linux/bits.h>
> > +
> >   #define CORESIGHT_ETM_PMU_NAME "cs_etm"
> >
> >   /*
> > @@ -38,4 +40,16 @@
> >   #define ETM4_CFG_BIT_RETSTK 12
> >   #define ETM4_CFG_BIT_VMID_OPT       15
> >
> > +/*
> > + * Interpretation of the PERF_RECORD_AUX_OUTPUT_HW_ID payload.
> > + * Used to associate a CPU with the CoreSight Trace ID.
> > + * [63:16] - unused SBZ
> > + * [15:08] - Trace ID
> > + * [07:00] - Version
>
> Could we please re-arrange the fields, such that it is easier to
> comprehend the TraceID looking at the raw trace dump ? Also to
> accommodate the future changes.
>
> e.g,
>        [15:00] - Trace ID        /* For future expansion, if at all */
>        [59:16] - RES0
>        [63:60] - Trace_ID_Version
>
> I think we *might* (not sure yet) end up adding "sinkid" when we have
> sink specific allocation, so that we can associate the HW_ID of an event
> to the "AUXTRACE" record (i.e., trace buffer).
>

If we go to per sink trace ID maps, then I can't see how we could
avoid needing some sort of ID in here, unless we can determine some
other method of specifying which CPUs traced into which trace buffer.

> So if we need to do that we could:
>
>        [15:00] - Trace ID        /* For future expansion, if at all */
>        [47:16] - Trace Pool ID( == 0 if global, == sink_id if sink based)
>        [59:48] - RES0
>        [63:60] - Trace_ID_Version == 1
>
> Or we could adopt the above straight away.
>

I wouldn't want to commit to a size for the sink ID yet. And I would
leave trace ID at what it is for now (8 bits).
Make the fields represent what is and up-version and update when
changes are actually required.
I think this packet may be a candidate for delivering other trace
related info we may need in future - such as the timestamp source that
is being worked on?

Mike

> Thoughts ?
>
> Suzuki
>
> > + */
> > +#define CS_AUX_HW_ID_VERSION_MASK    GENMASK_ULL(7, 0)
> > +#define CS_AUX_HW_ID_TRACE_ID_MASK   GENMASK_ULL(15, 8)
> > +
> > +#define CS_AUX_HW_ID_CURR_VERSION 0
>
>
> > +
> >   #endif
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK