linux-kernel - Re: [PATCH v3 00/15] Legacy hardware/cache events as json

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Message-ID: <03b13088-8dae-4d68-8594-6523b4aee406@linux.ibm.com>
Date: Wed, 3 Sep 2025 10:06:44 +0200
From: Thomas Richter <tmricht@...ux.ibm.com>
To: Ian Rogers <irogers@...gle.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>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        James Clark <james.clark@...aro.org>, Xu Yang <xu.yang_2@....com>,
        Thomas Falcon <thomas.falcon@...el.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org,
        Atish Patra <atishp@...osinc.com>, Beeman Strong <beeman@...osinc.com>,
        Leo Yan <leo.yan@....com>, Vince Weaver <vincent.weaver@...ne.edu>
Subject: Re: [PATCH v3 00/15] Legacy hardware/cache events as json

On 8/28/25 22:59, Ian Rogers wrote:
> Mirroring similar work for software events in commit 6e9fa4131abb
> ("perf parse-events: Remove non-json software events"). These changes
> migrate the legacy hardware and cache events to json.  With no hard
> coded legacy hardware or cache events the wild card, case
> insensitivity, etc. is consistent for events. This does, however, mean
> events like cycles will wild card against all PMUs. A change doing the
> same was originally posted and merged from:
> https://lore.kernel.org/r/20240416061533.921723-10-irogers@google.com
> and reverted by Linus in commit 4f1b067359ac ("Revert "perf
> parse-events: Prefer sysfs/JSON hardware events over legacy"") due to
> his dislike for the cycles behavior on ARM with perf record. Earlier
> patches in this series make perf record event opening failures
> non-fatal and hide the cycles event's failure to open on ARM in perf
> record, so it is expected the behavior will now be transparent in perf
> record on ARM. perf stat with a cycles event will wildcard open the
> event on all PMUs.
> 
> The change to support legacy events with PMUs was done to clean up
> Intel's hybrid PMU implementation. Having sysfs/json events with
> increased priority to legacy was requested by Mark Rutland
>  <mark.rutland@....com> to fix Apple-M PMU issues wrt broken legacy
> events on that PMU. It is believed the PMU driver is now fixed, but
> this has only been confirmed on ARM Juno boards. It was requested that
> RISC-V be able to add events to the perf tool json so the PMU driver
> didn't need to map legacy events to config encodings:
> https://lore.kernel.org/lkml/20240217005738.3744121-1-atishp@rivosinc.com/
> This patch series achieves this.
> 
> A previous series of patches decreasing legacy hardware event
> priorities was posted in:
> https://lore.kernel.org/lkml/20250416045117.876775-1-irogers@google.com/
> Namhyung Kim <namhyung@...nel.org> mentioned that hardware and
> software events can be implemented similarly:
> https://lore.kernel.org/lkml/aIJmJns2lopxf3EK@google.com/
> and this patch series achieves this.
> 
> Note, patch 1 (perf parse-events: Fix legacy cache events if event is
> duplicated in a PMU) fixes a function deleted by patch 15 (perf
> parse-events: Remove hard coded legacy hardware and cache
> parsing). Adding the json exposed an issue when legacy cache (not
> legacy hardware) and sysfs/json events exist. The fix is necessary to
> keep tests passing through the series. It is also posted for backports
> to stable trees.
> 
> The perf list behavior includes a lot more information and events. The
> before behavior on a hybrid alderlake is:


.....

For s390 the whole series:

Tested-by: Thomas Richter <tmricht@...ux.ibm.com>
-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

Vorsitzender des Aufsichtsrats: Wolfgang Wendt

Geschäftsführung: David Faller

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