linux-kernel - Re: [PATCH 1/2] perf/ibs: Fix interface via core pmu events

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Date:   Mon, 6 Mar 2023 14:29:10 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     peterz@...radead.org, eranian@...gle.com, acme@...nel.org,
        mark.rutland@....com, jolsa@...nel.org, irogers@...gle.com,
        bp@...en8.de, x86@...nel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, sandipan.das@....com,
        ananth.narayan@....com, santosh.shukla@....com
Subject: Re: [PATCH 1/2] perf/ibs: Fix interface via core pmu events

On Thu, Mar 2, 2023 at 9:54 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>
> Hi Namhyung,
>
> >> diff --git a/kernel/events/core.c b/kernel/events/core.c
> >> index a5a51dfdd622..c3f59d937280 100644
> >> --- a/kernel/events/core.c
> >> +++ b/kernel/events/core.c
> >> @@ -11633,9 +11633,13 @@ static struct pmu *perf_init_event(struct perf_event *event)
> >>                         goto fail;
> >>
> >>                 ret = perf_try_init_event(pmu, event);
> >> -               if (ret == -ENOENT && event->attr.type != type && !extended_type) {
> >> -                       type = event->attr.type;
> >> -                       goto again;
> >> +               if (ret == -ENOENT) {
> >> +                       if (event->attr.type != type && !extended_type) {
> >> +                               type = event->attr.type;
> >> +                               goto again;
> >> +                       }
> >> +                       if (pmu->capabilities & PERF_PMU_CAP_FORWARD_EVENT)
> >> +                               goto try_all;
> >
> > Wouldn't it be better to use a different error code to indicate
> > it's about precise_ip (or forwarding in general)?  Otherwise
> > other invalid config might cause the forwarding unnecessarily..
>
> That would make things easier and we might not need this new capability.
> Most appropriate error codes seems ENOENT, EOPNOTSUPP and EINVAL but all
> are already used for other purposes. Any other suggestions?

Maybe we can have more liberty for the error code since
it's not returned to the user.  How about ESRCH, EIO or ENXIO?

Thanks,
Namhyung