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

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Date: Mon, 13 May 2024 09:22:57 -0700
From: Ian Rogers <irogers@...gle.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Kan Liang <kan.liang@...ux.intel.com>, Thomas Richter <tmricht@...ux.ibm.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Jonathan Corbet <corbet@....net>, 
	Jing Zhang <renyu.zj@...ux.alibaba.com>, James Clark <james.clark@....com>, 
	Ravi Bangoria <ravi.bangoria@....com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v5 2/6] perf Document: Sysfs event names must be lower or
 upper case

On Sun, May 12, 2024 at 3:08 PM Randy Dunlap <rdunlap@...radead.org> 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@...gle.com>
> > Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
> > ---
> >  .../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
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