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.
v5: Follow Namhyung's suggestion and ignore the case where command
line dummy events fail to open alongside other events that all
fail to open. Note, the Tested-by tags are left on the series as
v4 and v5 were changing an error case that doesn't occur in
testing but was manually tested by myself.
v4: Rework the no events opening change from v3 to make it handle
multiple dummy events. Sadly an evlist isn't empty if it just
contains dummy events as the dummy event may be used with "perf
record -e dummy .." as a way to determine whether permission
issues exist. Other software events like cpu-clock would suffice
for this, but the using dummy genie has left the bottle.
Another problem is that we appear to have an excessive number of
dummy events added, for example, we can likely avoid a dummy event
and add sideband data to the original event. For auxtrace more
dummy events may be opened too. Anyway, this has led to the
approach taken in patch 3 where the number of dummy parsed events
is computed. If the number of removed/failing-to-open non-dummy
events matches the number of non-dummy events then we want to
fail, but only if there are no parsed dummy events or if there was
one then it must have opened. The math here is hard to read, but
passes my manual testing.
v3: Make no events opening for perf record a failure as suggested by
James Clark and Aditya Bodkhe <Aditya.Bodkhe1@xxxxxxx>. Also,
rebase.
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 | 47 ++++++++++++++++++---
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, 169 insertions(+), 74 deletions(-)
--
2.47.1.613.gc27f4b7a9f-goog
