linux-kernel - Re: [PATCH v4 00/14] perf cs-etm/arm-spe: Remove hard coded config fields

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Message-ID: <aWaysdXYIWi4nB1D@x1>
Date: Tue, 13 Jan 2026 18:01:37 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: James Clark <james.clark@...aro.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
	Leo Yan <leo.yan@...ux.dev>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, Leo Yan <leo.yan@....com>
Subject: Re: [PATCH v4 00/14] perf cs-etm/arm-spe: Remove hard coded config
 fields

On Mon, Dec 22, 2025 at 03:14:25PM +0000, James Clark wrote:
> The specific config field that an event format attribute is in is
> consistently hard coded, even though the API is supposed to be that the
> driver publishes the config field name. To stop this pattern from being
> copy pasted and causing problems in the future, replace them all with
> calls to a new helper that returns the value that a user set.
> 
> This reveals some issues in evsel__set_config_if_unset(). It doesn't
> work with sparse bitfields, which are an unused but documented feature.
> And it also only writes to the attr.config field. To fix it we need to
> start tracking user changes for all config fields and then use existing
> helper functions that support sparse bitfields. Some other refactoring
> was also required and a test was added.

Thanks, applied to perf-tools-next,

- Arnaldo
 
> ---
> Changes in v4:
> - Constify some function args (Ian)
> - Move some evsel__* functions to evsel.c and make some pmu.c functions
>   public to support this (Ian)
> - Drop pmu arg where it can be fetched from evsel->pmu (Ian)
> - Link to v3: https://lore.kernel.org/r/20251212-james-perf-config-bits-v3-0-aa36a4846776@linaro.org
> 
> Changes in v3:
> - Fix uninitialized variable warning on GCC
> - Fix leak of evlist in test
> - Confirm no type punning issues with ubsan (Ian)
> - Link to v2: https://lore.kernel.org/r/20251208-james-perf-config-bits-v2-0-4ac0281993b0@linaro.org
> 
> Changes in v2:
> - Remove macros in get_config_chgs() and some other refactoring.
> - Support sparse bitfields in evsel__set_config_if_unset().
> - Always track user changes instead of only when
>   'pmu->perf_event_attr_init_default' is set.
> - Add a test.
> - Don't bail out in cs-etm.c if any format fields are missing (Leo).
> - Rename 'guess' to 'synth' (Mike).
> - Link to v1: https://lore.kernel.org/r/20251201-james-perf-config-bits-v1-0-22ecbbf8007c@linaro.org
> 
> ---
> James Clark (14):
>       perf parse-events: Refactor get_config_terms() to remove macros
>       perf evsel: Refactor evsel__set_config_if_unset() arguments
>       perf evsel: Move evsel__* functions to evsel.c
>       perf evsel: Support sparse fields in evsel__set_config_if_unset()
>       perf parse-events: Track all user changed config bits
>       perf evsel: apply evsel__set_config_if_unset() to all config fields
>       perf evsel: Add a helper to get the value of a config field
>       perf parse-events: Always track user config changes
>       perf tests: Test evsel__set_config_if_unset() and config change tracking
>       perf cs-etm: Make a helper to find the Coresight evsel
>       perf cs-etm: Don't use hard coded config bits when setting up ETMCR
>       perf cs-etm: Don't use hard coded config bits when setting up TRCCONFIGR
>       perf cs-etm: Don't hard code config attribute when configuring the event
>       perf arm-spe: Don't hard code config attribute
> 
>  tools/perf/arch/arm/util/cs-etm.c    | 201 +++++++++++++++-------------
>  tools/perf/arch/arm64/util/arm-spe.c |  17 +--
>  tools/perf/arch/x86/util/intel-pt.c  |   3 +-
>  tools/perf/tests/pmu.c               |  91 +++++++++++++
>  tools/perf/util/evsel.c              | 112 +++++++++++++++-
>  tools/perf/util/evsel.h              |   6 +-
>  tools/perf/util/evsel_config.h       |   7 +-
>  tools/perf/util/parse-events.c       | 248 ++++++++++++++++++++---------------
>  tools/perf/util/pmu.c                |  95 ++++----------
>  tools/perf/util/pmu.h                |  34 ++++-
>  10 files changed, 529 insertions(+), 285 deletions(-)
> ---
> base-commit: cbd41c6d4c26c161a2b0e70ad411d3885ff13507
> change-id: 20251112-james-perf-config-bits-bee7106f0f00
> 
> Best regards,
> -- 
> James Clark <james.clark@...aro.org>
>