linux-kernel - Re: [PATCH 00/17] coresight: Use per-sink trace ID maps for Perf sessions

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Message-ID: <26bbc8c7-befc-4d2a-baf3-2156c740bbc9@os.amperecomputing.com>
Date: Tue, 7 May 2024 16:32:48 +0530
From: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
To: James Clark <james.clark@....com>, linux-perf-users@...r.kernel.org,
 scclevenger@...amperecomputing.com, coresight@...ts.linaro.org,
 suzuki.poulose@....com, mike.leach@...aro.org
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, John Garry
 <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
 Leo Yan <leo.yan@...ux.dev>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 00/17] coresight: Use per-sink trace ID maps for Perf
 sessions


Hi James,

On 29-04-2024 08:51 pm, James Clark wrote:
> This will allow sessions with more than CORESIGHT_TRACE_IDS_MAX ETMs
> as long as there are fewer than that many ETMs connected to each sink.
> 
> Each sink owns its own trace ID map, and any Perf session connecting to
> that sink will allocate from it, even if the sink is currently in use by
> other users. This is similar to the existing behavior where the dynamic
> trace IDs are constant as long as there is any concurrent Perf session
> active. It's not completely optimal because slightly more IDs will be
> used than necessary, but the optimal solution involves tracking the PIDs
> of each session and allocating ID maps based on the session owner. This
> is difficult to do with the combination of per-thread and per-cpu modes
> and some scheduling issues. The complexity of this isn't likely to worth
> it because even with multiple users they'd just see a difference in the
> ordering of ID allocations rather than hitting any limits (unless the
> hardware does have too many ETMs connected to one sink).
> 
> Per-thread mode works but only until there are any overlapping IDs, at
> which point Perf will error out. Both per-thread mode and sysfs mode are
> left to future changes, but both can be added on top of this initial
> implementation and only sysfs mode requires further driver changes.
> 
> The HW_ID version field hasn't been bumped in order to not break Perf
> which already has an error condition for other values of that field.
> Instead a new minor version has been added which signifies that there
> are new fields but the old fields are backwards compatible.
> 
> 
> James Clark (17):
>    perf cs-etm: Print error for new PERF_RECORD_AUX_OUTPUT_HW_ID versions
>    perf auxtrace: Allow number of queues to be specified
>    perf: cs-etm: Create decoders after both AUX and HW_ID search passes
>    perf: cs-etm: Allocate queues for all CPUs
>    perf: cs-etm: Move traceid_list to each queue
>    perf: cs-etm: Create decoders based on the trace ID mappings
>    perf: cs-etm: Support version 0.1 of HW_ID packets
>    coresight: Remove unused stubs
>    coresight: Clarify comments around the PID of the sink owner
>    coresight: Move struct coresight_trace_id_map to common header
>    coresight: Expose map argument in trace ID API
>    coresight: Make CPU id map a property of a trace ID map
>    coresight: Pass trace ID map into source enable
>    coresight: Use per-sink trace ID maps for Perf sessions
>    coresight: Remove pending trace ID release mechanism
>    coresight: Re-emit trace IDs when the sink changes in per-thread mode
>    coresight: Emit HW_IDs for all ETMs that are using the sink
> 
>   drivers/hwtracing/coresight/coresight-core.c  |  10 +
>   drivers/hwtracing/coresight/coresight-dummy.c |   3 +-
>   .../hwtracing/coresight/coresight-etm-perf.c  |  82 ++-
>   .../hwtracing/coresight/coresight-etm-perf.h  |  20 +-
>   .../coresight/coresight-etm3x-core.c          |  14 +-
>   .../coresight/coresight-etm4x-core.c          |  14 +-
>   drivers/hwtracing/coresight/coresight-stm.c   |   3 +-
>   drivers/hwtracing/coresight/coresight-sysfs.c |   3 +-
>   .../hwtracing/coresight/coresight-tmc-etr.c   |   5 +-
>   drivers/hwtracing/coresight/coresight-tmc.h   |   5 +-
>   drivers/hwtracing/coresight/coresight-tpdm.c  |   3 +-
>   .../hwtracing/coresight/coresight-trace-id.c  | 107 +--
>   .../hwtracing/coresight/coresight-trace-id.h  |  57 +-
>   include/linux/coresight-pmu.h                 |  17 +-
>   include/linux/coresight.h                     |  20 +-
>   tools/include/linux/coresight-pmu.h           |  17 +-
>   tools/perf/util/auxtrace.c                    |   9 +-
>   tools/perf/util/auxtrace.h                    |   1 +
>   .../perf/util/cs-etm-decoder/cs-etm-decoder.c |  28 +-
>   tools/perf/util/cs-etm.c                      | 617 ++++++++++++------
>   tools/perf/util/cs-etm.h                      |   2 +-
>   21 files changed, 633 insertions(+), 404 deletions(-)
> 

Thanks for implementing trace-id mapping per sink, with that we could 
try perf (coresight tracing) for more than 100+ CPUs.

Please feel free to add,
Tested-by: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>

Thanks,
Ganapat