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

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Message-ID: <21d108f2-db8e-457a-bbef-89d18e8d7601@linaro.org>
Date: Wed, 10 Sep 2025 12:14:11 +0100
From: James Clark <james.clark@...aro.org>
To: Ian Rogers <irogers@...gle.com>
Cc: 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>, 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 28/08/2025 9:59 pm, 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.

Hi Ian,

Briefly testing perf record and perf stat seem to work now. i.e "perf 
record -e cycles" doesn't fail and just skips the uncore cycles event. 
And "perf stat" now includes the uncore cycles event which I think is 
harmless.

But there are a few perf test failures. For example "test event parsing":

   evlist after sorting/fixing: 'arm_cmn_0/cycles/,{cycles,cache-
     misses,branch-misses}'
   FAILED tests/parse-events.c:1589 wrong number of entries
   Event test failure: test 57 '{cycles,cache-misses,branch-
     misses}:e'running test 58 'cycles/name=name/'

The tests "Perf time to TSC" and "Use a dummy software event to keep 
tracking" are using libperf to open the cycles event as a sampling event 
which now fails. It seems like we've fixed Perf record to ignore this 
failure, but we didn't think about libperf until now.

Thanks
James