Re: [PATCH] perf tests: Add auto counter reload (ACR) sampling test

[Ian Rogers]

On Wed, Apr 15, 2026 at 2:19 AM Mi, Dapeng <dapeng1.mi@xxxxxxxxxxxxxxx> wrote:
>
>
> On 4/13/2026 9:30 AM, Ian Rogers wrote:
> > On Sun, Apr 12, 2026 at 6:14 PM Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx> wrote:
> >> Add auto counter reload sampling test to verify that the intended event
> >> records can be captured and the self-reloaded events won't generate any
> >> records.
> >>
> >> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> >> ---
> >>  tools/perf/tests/shell/record.sh | 42 ++++++++++++++++++++++++++++++++
> >>  1 file changed, 42 insertions(+)
> >>
> >> diff --git a/tools/perf/tests/shell/record.sh b/tools/perf/tests/shell/record.sh
> >> index 7cb81cf3444a..1068843282f5 100755
> >> --- a/tools/perf/tests/shell/record.sh
> >> +++ b/tools/perf/tests/shell/record.sh
> >> @@ -402,6 +402,47 @@ test_callgraph() {
> >>    echo "Callgraph test [Success]"
> >>  }
> >>
> >> +test_acr_sampling() {
> >> +  events="{instructions/period=20000,acr_mask=0x2/u,cycles/period=40000,acr_mask=0x3/u}"
> >> +  pebs_events="{instructions/period=20000,acr_mask=0x2/pu,cycles/period=40000,acr_mask=0x3/u}"
> >> +  echo "Auto counter reload sampling test"
> >> +  if ! perf record -o "${perfdata}" -e "${events}" ${testprog} 2> /dev/null
> >> +  then
> >> +    echo "Auto counter reload sampling [Skipped not supported]"
> >> +    return
> >> +  fi
> >> +  if ! perf script -i "${perfdata}" | grep -q "period=20000,acr_mask=0x2"
> >> +  then
> >> +    echo "Auto counter reload sampling [Failed missing instructions event]"
> >> +    err=1
> >> +    return
> >> +  fi
> >> +  if perf script -i "${perfdata}" | grep -q "period=40000,acr_mask=0x3"
> >> +  then
> >> +    echo "Auto counter reload sampling [Failed cycles event shouldn't be sampled]"
> >> +    err=1
> >> +    return
> >> +  fi
> >> +  if ! perf record -o "${perfdata}" -e "${pebs_events}" ${testprog} 2> /dev/null
> >> +  then
> >> +    echo "Auto counter reload PEBS sampling [Skipped not supported]"
> >> +    return
> >> +  fi
> >> +  if ! perf script -i "${perfdata}" | grep -q "period=20000,acr_mask=0x2"
> >> +  then
> >> +    echo "Auto counter reload PEBS sampling [Failed missing instructions event]"
> >> +    err=1
> >> +    return
> >> +  fi
> >> +  if perf script -i "${perfdata}" | grep -q "period=40000,acr_mask=0x3"
> >> +  then
> >> +    echo "Auto counter reload PEBS sampling [Failed cycles event shouldn't be sampled]"
> >> +    err=1
> >> +    return
> >> +  fi
> >> +  echo "Auto counter reload sampling [Success]"
> > Thanks Dapeng! Could we also test ratio-to-prev as well as just the
> > plain acr_mask?
>
> Ian, it could be hard to validate ratio-to-prev option in this test. On
> platforms which don't support ACR, perf would automatically fallback the
> ACR sampling to normal sampling, this would lead to false positives on
> checking the existence of records from cycles event. I didn't find a good
> way to figure out this fallback.
>
> Since we already have independent test case to validate the ratio_to_prev
> parsing. It may be unnecessary to add ratio-to-prev validation in this ACR
> test.

So the ratio_to_prev test covers parsing the ratio-to-prev option (it
only has `perf record` commands) and ensures it is acted upon, but it
doesn't check the option's functional behavior - what the output is.
This test makes sure the acr_mask option is functional and so would be
complemented by ratio-to-prev testing somethig like:
```
  rtp_events="{instructions,cycles/period=40000,ratio-to-prev=0.5/u}"

  # Test ratio-to-prev
  if ! perf record -o "${perfdata}" -e "${rtp_events}" ${testprog} 2> /dev/null
  then
    echo "Auto counter reload ratio-to-prev sampling [Failed record
ratio-to-prev]"
    err=1
    return
  fi
  if ! perf script -i "${perfdata}" | grep -q "instructions"
  then
    echo "Auto counter reload ratio-to-prev sampling [Failed missing
instructions event]"
    err=1
    return
  fi
  if perf script -i "${perfdata}" | grep -q "cycles"
  then
    echo "Auto counter reload ratio-to-prev sampling [Failed cycles
event shouldn't be sampled]"
    err=1
    return
  fi
```
The first thing your test does is to make sure the acr_mask is
supported, so I'm not sure how the fall back can happen?
We could additionally check for
`/sys/bus/event_source/devices/cpu*/format/acr_mask`.

Thanks,
Ian

> >
> > Thanks,
> > Ian
> >
> >> +}
> >> +
> >>  test_ratio_to_prev() {
> >>    echo "ratio-to-prev test"
> >>    if ! perf record -o /dev/null -e "{instructions, cycles/period=100000,ratio-to-prev=0.5/}" \
> >> @@ -457,6 +498,7 @@ test_leader_sampling
> >>  test_topdown_leader_sampling
> >>  test_precise_max
> >>  test_callgraph
> >> +test_acr_sampling
> >>  test_ratio_to_prev
> >>
> >>  # restore the default value
> >>
> >> base-commit: 4e03d6494f9504f8af46ba68a2a8b6877c196789
> >> --
> >> 2.34.1
> >>