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perf evsel: Improve falling back from cycles

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Switch to using evsel__match rather than comparing perf_event_attr
values, this is robust on hybrid architectures.
Ensure evsel->pmu matches the evsel->core.attr.
Remove exclude bits that get set in other fallback attempts when
switching the event.
Log the event name with modifiers when switching the event on fallback.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
This commit is contained in:
Ian Rogers
2026-03-18 16:45:56 -07:00
committed by Namhyung Kim
parent a90407a5a8
commit d84db579d7
2 changed files with 33 additions and 14 deletions
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45
tools/perf/util/evsel.c
View File

@@ -3785,25 +3785,42 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
{
int paranoid;
if ((err == ENOENT || err == ENXIO || err == ENODEV) &&
evsel->core.attr.type == PERF_TYPE_HARDWARE &&
evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
if ((err == ENODEV || err == ENOENT || err == ENXIO) &&
evsel__match(evsel, HARDWARE, HW_CPU_CYCLES)) {
/*
* If it's cycles then fall back to hrtimer based cpu-clock sw
* counter, which is always available even if no PMU support.
*
* PPC returns ENXIO until 2.6.37 (behavior changed with commit
* b0a873e).
* If it's the legacy hardware cycles event fails then fall back
* to hrtimer based cpu-clock sw counter, which is always
* available even if no PMU support. PPC returned ENXIO rather
* than ENODEV or ENOENT until 2.6.37.
*/
evsel->core.attr.type = PERF_TYPE_SOFTWARE;
evsel->pmu = perf_pmus__find_by_type(PERF_TYPE_SOFTWARE);
assert(evsel->pmu); /* software is a "well-known" and can't fail PMU type. */
/* Configure the event. */
evsel->core.attr.type = PERF_TYPE_SOFTWARE;
evsel->core.attr.config = target__has_cpu(target)
? PERF_COUNT_SW_CPU_CLOCK
: PERF_COUNT_SW_TASK_CLOCK;
scnprintf(msg, msgsize,
"The cycles event is not supported, trying to fall back to %s",
target__has_cpu(target) ? "cpu-clock" : "task-clock");
evsel->core.is_pmu_core = false;
/* Remove excludes for new event. */
if (evsel->fallenback_eacces) {
evsel->core.attr.exclude_kernel = 0;
evsel->core.attr.exclude_hv = 0;
evsel->fallenback_eacces = false;
}
if (evsel->fallenback_eopnotsupp) {
evsel->core.attr.exclude_guest = 0;
evsel->fallenback_eopnotsupp = false;
}
/* Name is recomputed by evsel__name. */
zfree(&evsel->name);
/* Log message. */
scnprintf(msg, msgsize,
"The cycles event is not supported, trying to fall back to %s",
evsel__name(evsel));
return true;
} else if (err == EACCES && !evsel->core.attr.exclude_kernel &&
(paranoid = perf_event_paranoid()) > 1) {
@@ -3830,7 +3847,7 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
" samples", paranoid);
evsel->core.attr.exclude_kernel = 1;
evsel->core.attr.exclude_hv = 1;
evsel->fallenback_eacces = true;
return true;
} else if (err == EOPNOTSUPP && !evsel->core.attr.exclude_guest &&
!evsel->exclude_GH) {
@@ -3851,7 +3868,7 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
/* Apple M1 requires exclude_guest */
scnprintf(msg, msgsize, "Trying to fall back to excluding guest samples");
evsel->core.attr.exclude_guest = 1;
evsel->fallenback_eopnotsupp = true;
return true;
}
no_fallback:

2
tools/perf/util/evsel.h
View File

@@ -124,6 +124,8 @@ struct evsel {
bool default_metricgroup; /* A member of the Default metricgroup */
bool default_show_events; /* If a default group member, show the event */
bool needs_uniquify;
bool fallenback_eacces;
bool fallenback_eopnotsupp;
struct hashmap *per_pkg_mask;
int err;
int script_output_type;