Re: [PATCH v5 2/6] perf Document: Sysfs event names must be lower or upper case

[Ian Rogers]

On Sun, May 12, 2024 at 3:08 PM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>
> Hi,
>
> On 5/2/24 2:35 PM, Ian Rogers wrote:
> > To avoid directory scans in perf it is going to be assumed that sysfs
> > event names are either lower or upper case.
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > Reviewed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > ---
> >  .../ABI/testing/sysfs-bus-event_source-devices-events       | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-event_source-devices-events b/Documentation/ABI/testing/sysfs-bus-event_source-devices-events
> > index 77de58d03822..e7efeab2ee83 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-event_source-devices-events
> > +++ b/Documentation/ABI/testing/sysfs-bus-event_source-devices-events
> > @@ -37,6 +37,12 @@ Description:       Per-pmu performance monitoring events specific to the running syste
> >               performance monitoring event supported by the <pmu>. The name
> >               of the file is the name of the event.
> >
> > +             As performance monitoring event names are case
> > +             insensitive in the perf tool, the perf tool only looks
> > +             for lower or upper case event names in sysfs to avoid
> > +             scanning the directory. It is therefore required the
> > +             name of the event here is either lower or upper case.
> > +
>
> This is ambiguous to me. Is it clear to everyone else?
>
> "for lower or upper case event names":
>
> Is that a logical OR or an exclusive OR?
> "AbC" contains lower case or upper case characters. :)
>
> I think the code [static bool permitted_event_name()]
> implements an exclusive OR.
> The code also allows event names to contain numbers AFAICT.
> The documentation doesn't mention this.
>
> HTH.
>
> >               File contents:
> >
> >                       <term>[=<value>][,<term>[=<value>]]...

Sorry, this reads like a troll. Assuming good intentions, could you
propose a fix in the form of a patch? When a word is made upper or
lower case I believe it is generally assumed the operation applies to
all characters within the word, but I'm happy to see ambiguity cleared
up.

Thanks,
Ian

> --
> #Randy
> https://people.kernel.org/tglx/notes-about-netiquette
> https://subspace.kernel.org/etiquette.html