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Date:   Thu, 21 Jul 2022 11:27:47 +0100
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Subject: Re: [PATCH v2 00/13] coresight: Add new API to allocate trace source
 ID values
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To:     Mike Leach <mike.leach@linaro.org>
Cc:     mathieu.poirier@linaro.org, peterz@infradead.org, mingo@redhat.com,
        acme@kernel.org, linux-perf-users@vger.kernel.org,
        quic_jinlmao@quicinc.com, suzuki.poulose@arm.com,
        coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <20220704081149.16797-1-mike.leach@linaro.org>
From:   James Clark <james.clark@arm.com>
In-Reply-To: <20220704081149.16797-1-mike.leach@linaro.org>
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On 04/07/2022 09:11, Mike Leach wrote:
> The current method for allocating trace source ID values to sources is
> to use a fixed algorithm for CPU based sources of (cpu_num * 2 + 0x10).
> The STM is allocated ID 0x1.
> 
> This fixed algorithm is used in both the CoreSight driver code, and by
> perf when writing the trace metadata in the AUXTRACE_INFO record.
> 
> The method needs replacing as currently:-
> 1. It is inefficient in using available IDs.
> 2. Does not scale to larger systems with many cores and the algorithm
> has no limits so will generate invalid trace IDs for cpu number > 44.
> 
> Additionally requirements to allocate additional system IDs on some
> systems have been seen.
> 
> This patch set  introduces an API that allows the allocation of trace IDs
> in a dynamic manner.

I've tested this with various commands like with per-thread mode, attaching,
running the tests and also Carsten's new tests. Apart from the possible
backwards compatibility issue and the minor code comments it looks good to
me.

> 
> Architecturally reserved IDs are never allocated, and the system is
> limited to allocating only valid IDs.
> 
> Each of the current trace sources ETM3.x, ETM4.x and STM is updated to use
> the new API.
> 
> For the ETMx.x devices IDs are allocated on certain events
> a) When using sysfs, an ID will be allocated on hardware enable, or a read of
> sysfs TRCTRACEID register and freed when the sysfs reset is written.
> 
> b) When using perf, ID is allocated on hardware enable, and freed on
> hardware disable. IDs are communicated using the AUX_OUTPUT_HW_ID packet.
> The ID allocator is notified when perf sessions start and stop
> so CPU based IDs are kept constant throughout any perf session.
> 
> 
> Note: This patchset breaks backward compatibility for perf record and
> perf report.
> 
> Because the method for generating the AUXTRACE_INFO meta data has
> changed, using an older perf record will result in metadata that
> does not match the trace IDs used in the recorded trace data.
> This mismatch will cause subsequent decode to fail.
> 
> The version of the AUXTRACE_INFO has been updated to reflect the fact that
> the trace source IDs are no longer present in the metadata. This will
> mean older versions of perf report cannot decode the file.
> 
> Applies to coresight/next [c06475910b52]
> Tested on DB410c
> 
> Changes since v1:
> (after feedback & discussion with Mathieu & Suzuki).
> 
> 1) API has changed. The global trace ID map is managed internally, so it
> is no longer passed in to the API functions.
> 
> 2) perf record does not use sysfs to find the trace IDs. These are now
> output as AUX_OUTPUT_HW_ID events. The drivers, perf record, and perf report
> have been updated accordingly to generate and handle these events.
> 
> Mike Leach (13):
>   coresight: trace-id: Add API to dynamically assign Trace ID values
>   coresight: trace-id: update CoreSight core to use Trace ID API
>   coresight: stm: Update STM driver to use Trace ID API
>   coresight: etm4x: Update ETM4 driver to use Trace ID API
>   coresight: etm3x: Update ETM3 driver to use Trace ID API
>   coresight: etmX.X: stm: Remove unused legacy source Trace ID ops
>   coresight: perf: traceid: Add perf notifiers for Trace ID
>   perf: cs-etm: Move mapping of Trace ID and cpu into helper function
>   perf: cs-etm: Update record event to use new Trace ID protocol
>   kernel: events: Export perf_report_aux_output_id()
>   perf: cs-etm: Handle PERF_RECORD_AUX_OUTPUT_HW_ID packet
>   coresight: events: PERF_RECORD_AUX_OUTPUT_HW_ID used for Trace ID
>   coresight: trace-id: Add debug & test macros to Trace ID allocation
> 
>  drivers/hwtracing/coresight/Makefile          |   2 +-
>  drivers/hwtracing/coresight/coresight-core.c  |  49 +---
>  .../hwtracing/coresight/coresight-etm-perf.c  |  17 ++
>  drivers/hwtracing/coresight/coresight-etm.h   |   3 +-
>  .../coresight/coresight-etm3x-core.c          |  85 +++---
>  .../coresight/coresight-etm3x-sysfs.c         |  28 +-
>  .../coresight/coresight-etm4x-core.c          |  65 ++++-
>  .../coresight/coresight-etm4x-sysfs.c         |  32 ++-
>  drivers/hwtracing/coresight/coresight-etm4x.h |   3 +
>  drivers/hwtracing/coresight/coresight-stm.c   |  49 +---
>  .../hwtracing/coresight/coresight-trace-id.c  | 263 ++++++++++++++++++
>  .../hwtracing/coresight/coresight-trace-id.h  |  65 +++++
>  include/linux/coresight-pmu.h                 |  31 ++-
>  include/linux/coresight.h                     |   3 -
>  kernel/events/core.c                          |   1 +
>  tools/include/linux/coresight-pmu.h           |  31 ++-
>  tools/perf/arch/arm/util/cs-etm.c             |  21 +-
>  .../perf/util/cs-etm-decoder/cs-etm-decoder.c |   9 +
>  tools/perf/util/cs-etm.c                      | 220 +++++++++++++--
>  tools/perf/util/cs-etm.h                      |  14 +-
>  20 files changed, 784 insertions(+), 207 deletions(-)
>  create mode 100644 drivers/hwtracing/coresight/coresight-trace-id.c
>  create mode 100644 drivers/hwtracing/coresight/coresight-trace-id.h
>