linux-kernel - Re: perf tool: About tests debug level

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Date:   Tue, 22 Jun 2021 09:00:31 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     John Garry <john.garry@...wei.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <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>,
        Namhyung Kim <namhyung@...nel.org>,
        Jin Yao <yao.jin@...ux.intel.com>
Subject: Re: perf tool: About tests debug level

On Tue, Jun 22, 2021 at 4:58 AM John Garry <john.garry@...wei.com> wrote:
>
> On 22/06/2021 06:04, Ian Rogers wrote:
> >> ---- end ----
> >> Parse and process metrics: FAILED!
> >>
> >> Note that the "FAILED" messages from the test code come from pr_debug().
> >>
> >> In a way, I feel that pr_debug()/err from the test is more important
> >> than pr_debug() from the core code (when running a test).
> >>
> >> Any opinion on this or how to improve (if anyone agrees with me)? Or am
> >> I missing something? Or is it not so important?
> > Hi John,
> >
>
> Hi Ian,
>
> > I think the issue is that in the parsing you don't know it's broken
> > until something goes wrong. Putting everything on pr_err would cause
> > spam in the not broken case.
>
> Right, I would not suggest using pr_err everywhere.
>
> > Improving the parsing error handling is a
> > big task with lex and yacc to some extent getting in the way. Perhaps
> > a middle way is to have a parameter to the parser that logs more, and
> > recursively call this in the parser when parsing fails. I guess there
> > is also a danger of a performance hit.
>
> So I am thinking that for running a test, -v means different levels logs
> for test code and for core (non-test code). For example, -v prints
> pr_warn() and higher for test logs, but nothing for core logs. And then
> -vv for running a test gives pr_debug and above for test logs, and
> pr_warn and above for core logs. Or something like that.
>
> Maybe that is not a good idea. But I'm just saying that it's hard to
> debug currently at -v for tests.
>
> Thanks,
> John

I think this sounds good. It'd be nice also to have verbose output in
the shell tests following the same convention. There's currently no
verbose logging in shell tests but I propose it here:
https://lore.kernel.org/lkml/20210621215648.2991319-1-irogers@google.com/
By their nature some of the shell tests launch perf, perhaps there can
be some convention on passing the verbose flag through in those cases.

Thanks,
Ian