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 11:54:29 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Ian Rogers <irogers@...gle.com>
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 5/13/24 9:22 AM, Ian Rogers wrote:
> 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

Sure, I'll send a patch.
No trolling here.

> 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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