[v2,0/4] Prefer sysfs/JSON events also when no PMU is provided

Message

Ian Rogers Nov. 13, 2024, 1:19 a.m. UTC

At the RISC-V summit the topic of avoiding event data being in the
RISC-V PMU kernel driver came up. There is a preference for sysfs/JSON
events being the priority when no PMU is provided so that legacy
events maybe supported via json. Originally Mark Rutland also
expressed at LPC 2023 that doing this would resolve bugs on ARM Apple
M? processors, but James Clark more recently tested this and believes
the driver issues there may not have existed or have been resolved. In
any case, it is inconsistent that with a PMU event names avoid legacy
encodings, but when wildcarding PMUs (ie without a PMU with the event
name) the legacy encodings have priority.

The patch doing this work was reverted in a v6.10 release candidate
as, even though the patch was posted for weeks and had been on
linux-next for weeks without issue, Linus was in the habit of using
explicit legacy events with unsupported precision options on his
Neoverse-N1. This machine has SLC PMU events for bus and CPU cycles
where ARM decided to call the events bus_cycles and cycles, the latter
being also a legacy event name. ARM haven't renamed the cycles event
to a more consistent cpu_cycles and avoided the problem. With these
changes the problematic event will now be skipped, a large warning
produced, and perf record will continue for the other PMU events. This
solution was proposed by Arnaldo.

Two minor changes have been added to help with the error message and
to work around issues occurring with "perf stat metrics (shadow stat)
test".

The patches have only been tested on my x86 non-hybrid laptop.

v2: Rebase and add tested-by tags from James Clark, Leo Yan and Atish
    Patra who have tested on RISC-V and ARM CPUs, including the
    problem case from before.

Ian Rogers (4):
  perf evsel: Add pmu_name helper
  perf stat: Fix find_stat for mixed legacy/non-legacy events
  perf record: Skip don't fail for events that don't open
  perf parse-events: Reapply "Prefer sysfs/JSON hardware events over
    legacy"

 tools/perf/builtin-record.c    | 22 +++++++---
 tools/perf/util/evsel.c        | 10 +++++
 tools/perf/util/evsel.h        |  1 +
 tools/perf/util/parse-events.c | 26 +++++++++---
 tools/perf/util/parse-events.l | 76 +++++++++++++++++-----------------
 tools/perf/util/parse-events.y | 60 ++++++++++++++++++---------
 tools/perf/util/pmus.c         | 20 +++++++--
 tools/perf/util/stat-shadow.c  |  3 +-
 8 files changed, 145 insertions(+), 73 deletions(-)