linux-kernel - Re: [PATCH v2] perf jevents: Handle deleted JSONS in out of source builds

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Message-ID: <aXjwFhUEOUc7rNnZ@x1>
Date: Tue, 27 Jan 2026 14:04:22 -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>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v2] perf jevents: Handle deleted JSONS in out of source
 builds

On Wed, Jan 21, 2026 at 04:19:40PM +0000, James Clark wrote:
> Make the source folders a dependency for the generated folder root so
> that whenever a file is deleted from the source it will force a new
> fresh copy of all the JSON files and avoid stale deleted files.
> 
> JSON_DIRS_OUTPUT_ROOT needs to be a dependency of LEGACY_CACHE_JSON so
> that the root folder doesn't get cleaned after the legacy JSON is
> generated. But this is a no-op with in-source builds as
> JSON_DIRS_OUTPUT_ROOT is unset.
> 
> JSON_DIRS is added as a dependency of PMU_EVENTS_C which also forces a
> re-build for in source builds when JSON files are deleted. This could
> have also resulted in stale builds, but never a broken one.

Thanks, applied to perf-tools-next,

- Arnaldo
 
> Reported-by: Mark Brown <broonie@...nel.org>
> Closes: https://lore.kernel.org/linux-next/aW5XSAo88_LBPSYI@sirena.org.uk/
> Fixes: 4bb55de4ff03 ("perf jevents: Support copying the source json files to OUTPUT")
> Signed-off-by: James Clark <james.clark@...aro.org>
> ---
> This is a bit of a hack and I thought that making jevents.py handle
> multiple input folders would be a much better solution than this. Then
> we could have "gen-pmu-events" for only generated files and "pmu-events"
> for only in-tree input files. It would be very clear what's generated
> and what's not and all copying rules and special clean rules just
> disappear (and this isn't the first time these rules have caused build
> issues).
> 
> Unfortunately, after a while of trying to modify the script I thought it
> was too invasive for now. The script does output per-file at the very
> bottom of the logic in process_one_file(), so adding files in another
> folder ends up re-emitting section headers when another chunk is output.
> Although other parts of the script do build things up in memory before
> outputting so it was possible to make those parts work with multiple
> folders transparently.
> ---
> Changes in v2:
> - Drop dependency on rsync by wiping the output folder any time a source
>   folder is updated.
> - Also fix the same issue for in source builds by adding the source
>   folders as a dependency of PMU_EVENTS_C.
> - Link to v1: https://lore.kernel.org/r/20260120-james-perf-json-delete-fix-v1-1-bae2194b1dcf@linaro.org
> ---
>  tools/perf/pmu-events/Build | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
> index a46ab7b612df..4f9ef624ba70 100644
> --- a/tools/perf/pmu-events/Build
> +++ b/tools/perf/pmu-events/Build
> @@ -1,5 +1,6 @@
>  pmu-events-y	+= pmu-events.o
>  JSON		=  $(shell find pmu-events/arch -name '*.json' -o -name '*.csv')
> +JSON_DIRS	=  $(shell find pmu-events/arch -type d)
>  JDIR_TEST	=  pmu-events/arch/test
>  JSON_TEST	=  $(shell [ -d $(JDIR_TEST) ] &&			\
>  			find $(JDIR_TEST) -name '*.json')
> @@ -31,16 +32,23 @@ $(PMU_EVENTS_C): $(EMPTY_PMU_EVENTS_C)
>  else
>  # Copy checked-in json to OUTPUT for generation if it's an out of source build
>  ifneq ($(OUTPUT),)
> -$(OUTPUT)pmu-events/arch/%: pmu-events/arch/%
> +# Remove all output directories when any source directory timestamp changes
> +# so there are no stale deleted files
> +JSON_DIRS_ROOT = $(OUTPUT)pmu-events/arch/
> +$(JSON_DIRS_ROOT): $(JSON_DIRS)
> +	$(Q)$(call echo-cmd,gen)rm -rf $@
> +	$(Q)mkdir -p $@
> +
> +$(OUTPUT)pmu-events/arch/%: pmu-events/arch/% $(JSON_DIRS_ROOT)
>  	$(call rule_mkdir)
>  	$(Q)$(call echo-cmd,gen)cp $< $@
>  endif
>  
> -$(LEGACY_CACHE_JSON): $(LEGACY_CACHE_PY)
> +$(LEGACY_CACHE_JSON): $(LEGACY_CACHE_PY) $(JSON_DIRS_ROOT)
>  	$(call rule_mkdir)
>  	$(Q)$(call echo-cmd,gen)$(PYTHON) $(LEGACY_CACHE_PY) > $@
>  
> -GEN_JSON = $(patsubst %,$(OUTPUT)%,$(JSON)) $(LEGACY_CACHE_JSON)
> +GEN_JSON = $(patsubst %,$(OUTPUT)%,$(JSON)) $(LEGACY_CACHE_JSON) $(JSON_DIRS)
>  
>  $(METRIC_TEST_LOG): $(METRIC_TEST_PY) $(METRIC_PY)
>  	$(call rule_mkdir)
> 
> ---
> base-commit: 571d29baa07e83e637075239f379f91353c24ec9
> change-id: 20260120-james-perf-json-delete-fix-71553b379e8e
> 
> Best regards,
> -- 
> James Clark <james.clark@...aro.org>