linux-kernel - Re: [PATCH] perf: Fix "Track with sched_switch" test by not printing warnings in quiet mode

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Date:   Fri, 14 Oct 2022 10:47:34 +0100
From:   James Clark <james.clark@....com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     linux-perf-users <linux-perf-users@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] perf: Fix "Track with sched_switch" test by not printing
 warnings in quiet mode

On 13/10/2022 17:57, Namhyung Kim wrote:
> On Wed, Oct 12, 2022 at 10:12 AM James Clark <james.clark@....com> wrote:
>>
>>
>>
>> On 12/10/2022 17:50, Namhyung Kim wrote:
>>> On Wed, Oct 12, 2022 at 4:13 AM James Clark <james.clark@....com> wrote:
>>>>> The test already supplies -q to run in quiet mode, so extend quiet mode
>>>>> to perf_stdio__warning() and also ui__warning() for consistency.
>>>
>>> I'm not sure if suppressing the warnings with -q is a good thing.
>>> Maybe we need to separate warning/debug messages from the output.
>>
>> I don't see the issue with warnings being suppressed in quiet mode as
>> long as errors are still printed. In other cases warnings have already
>> been suppressed by quiet mode and this site is the odd one out.
>>
>> What use case are you thinking of where someone explicitly adds -q but
>> wants to see non fatal warnings?
> 
> I don't have any specific use case.  If it's already suppressed in other
> cases, I'm fine with it.
> 

Actually I may have been mistaken. Seems like quiet is only used for
"extra info" type messages rather than warnings. Although the commit
message does say:

  The -q/--quiet option is to suppress any message. Sometimes users just
  want to see the numbers and it can be used for that case.

With 'any' that I would take to include warnings as well. I could move
warnings to stderr, but this has a much greater chance of breaking
anyone's workflows that might be looking for warnings on stdout than
removing warnings when -q is provided.

Also if warnings are moved to stderr and quiet isn't used, there would
be no way to suppress warnings in the TUI which might actually be a
useful feature.

So I'm still leaning towards the original change, if you are ok with
that even though it's not done elsewhere?

> Thanks,
> Namhyung