Re: [PATCH v1] perf test stat: Avoid hybrid assumption when virtualized
From: James Clark
Date: Thu Dec 12 2024 - 10:51:49 EST
On 11/12/2024 5:58 pm, Ian Rogers wrote:
On Wed, Dec 11, 2024 at 1:50 AM James Clark <james.clark@xxxxxxxxxx> wrote:
On 11/12/2024 6:10 am, Ian Rogers wrote:
The cycles event will fallback to task-clock in the hybrid test when
running virtualized. Change the test to not fail for this.
Fixes: a6b8bb2addd0 ("perf test: Add a test for default perf stat command")
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
tools/perf/tests/shell/stat.sh | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/tools/perf/tests/shell/stat.sh b/tools/perf/tests/shell/stat.sh
index 5a2ca2bcf94d..60cea07350e1 100755
--- a/tools/perf/tests/shell/stat.sh
+++ b/tools/perf/tests/shell/stat.sh
@@ -165,9 +165,13 @@ test_hybrid() {
if [ "$pmus" -ne "$cycles_events" ]
then
- echo "hybrid test [Found $pmus PMUs but $cycles_events cycles events. Failed]"
- err=1
- return
+ # If virtualized the software task-clock event will be used.
+ if ! perf stat -- true 2>&1 | grep -q "task-clock"
+ then
+ echo "hybrid test [Found $pmus PMUs but $cycles_events cycles events. Failed]"
+ err=1
+ return
+ fi
fi
echo "hybrid test [Success]"
}
Hi Ian,
Isn't the distinction between task-clock and cpu-clock whether the event
is per-cpu or not?
$ perf stat -C 1 -- true 2>&1 | grep cpu-clock
1.49 msec cpu-clock # 0.917 CPUs utilized
$ perf stat -- true 2>&1 | grep task-clock
0.30 msec task-clock # 0.366 CPUs utilized
The test uses per-task mode so this change makes it always pass, even
when the number of cycles events doesn't match the PMUs.
So I'm confused by the test, but it has caused a passing test to be
broken for me when I run virtualized. The test is checking a cycles
event is opened on each hybrid PMU, but this is conflated with
checking perf stat's "default" output. The cycles event will fall back
to task-clock in per-task mode but we also open a task-clock in
default mode. Should:
```
if [ "$pmus" -ne "$cycles_events" ]
```
be something like this then:
```
# The expectation is that default output will have a cycles events on
each hybrid
# PMU, but in situations with no cycles PMU events, like
virtualized,this can fall
# back to task-clock and so the end count may be 0. Fail if neither
condition holds.
if [ "$pmus" -ne "$cycles_events" ] && [ "$pmus" -ne "0" ]
Yes it might make sense to skip this part if pmus == 0 then. Namhyung
suggested to always assume 1 PMU to cover platforms that don't publish
any PMU with the cpus file, but I suppose that breaks in this case.
If you still add the fallback check for task-clock it covers hybrid, 1
PMU and virtualized and we could even rename the test to
test_default_stat_2.
```
Thanks,
Ian