Messages in this thread | | | Date | Tue, 06 Sep 2022 17:56:37 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf test: Skip sigtrap test on old kernels |
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On September 6, 2022 5:50:05 PM GMT-03:00, Marco Elver <elver@google.com> wrote: >On Tue, 6 Sept 2022 at 20:31, Namhyung Kim <namhyung@kernel.org> wrote: >> >> On Tue, Sep 6, 2022 at 5:45 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote: >> > >> > Em Sat, Sep 03, 2022 at 08:52:01AM +0200, Marco Elver escreveu: >> > > On Sat, 3 Sept 2022 at 02:02, Namhyung Kim <namhyung@kernel.org> wrote: >> > > > >> > > > If it runs on an old kernel, perf_event_open would fail because of the >> > > > new fields sigtrap and sig_data. Just skip the test if it failed. >> > > > >> > > > Cc: Marco Elver <elver@google.com> >> > > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> >> > > > --- >> > > > tools/perf/tests/sigtrap.c | 1 + >> > > > 1 file changed, 1 insertion(+) >> > > > >> > > > diff --git a/tools/perf/tests/sigtrap.c b/tools/perf/tests/sigtrap.c >> > > > index e32ece90e164..7057566e6ae4 100644 >> > > > --- a/tools/perf/tests/sigtrap.c >> > > > +++ b/tools/perf/tests/sigtrap.c >> > > > @@ -140,6 +140,7 @@ static int test__sigtrap(struct test_suite *test __maybe_unused, int subtest __m >> > > > fd = sys_perf_event_open(&attr, 0, -1, -1, perf_event_open_cloexec_flag()); >> > > > if (fd < 0) { >> > > > pr_debug("FAILED sys_perf_event_open(): %s\n", str_error_r(errno, sbuf, sizeof(sbuf))); >> > > > + ret = TEST_SKIP; >> > > >> > > Wouldn't we be interested if perf_event_open() fails because it could >> > > actually be a bug? By skipping we'll be more likely to miss the fact >> > > there's a real problem. >> > > >> > > That's my naive thinking at least - what do other perf tests usually >> > > do in this case? >> > >> > Yeah, I was going to try and check if this is the only way that, with >> > the given arguments, perf_event_open would fail, but its better to at >> > least check errno against -EINVAL or something? >> >> EINVAL would be too generic and the kernel returns it in many places. >> I really wish we could have a better error reporting mechanism. >> >> Maybe we could retry perf_event_open with sigtrap and sig_data cleared. >> If it succeeded, then we can skip the test. If it still failed, then report >> the error. But it still couldn't find a bug in the sigtrap code. >> What do you think? > >Yes, that's what I meant, that it could point out an issue with >sigtrap perf_event_open(). > >If there's no clear way to determine if it's just not supported or a >bug, it'd be better to leave it as-is.
perf could go fancy and try to add a probe using a source file+line where older kernels would fail 8-)
Anyway, perf already does all sorts of kernel capability checks, perhaps this is one of can for sure detect it's something available :-/
One new way could be to look at BTF?
> >Some other options: > >1. Provide a way to disable certain tests, if it's known they will >fail for otherwise benign reasons i.e. no support. > >2. Provide a command line option to skip instead of fail tests where >perf_event_open() returns some particular errnos. The default will be >fail, but you can then choose to trust that failure of >perf_event_open() means no support, and pass the option.
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