linux-kernel - Re: [PATCH] perf tool: Fix output unexpected messages in quiet mode

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Date:   Mon, 19 Dec 2022 12:28:20 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Yang Jihong <yangjihong1@...wei.com>, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com, kan.liang@...ux.intel.com,
        kim.phillips@....com, german.gomez@....com, ravi.bangoria@....com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tool: Fix output unexpected messages in quiet mode

On 19/12/22 11:28, Yang Jihong wrote:
> Hello,
> 
> On 2022/12/19 14:59, Adrian Hunter wrote:
>> On 19/12/22 04:49, Yang Jihong wrote:
>>> When perf uses quiet mode, perf_quiet_option sets debug_peo_args to -1,
>>
>> Seems like redirect_to_stderr has similar issue?
> The redirect_to_stderr is used only in the veprintf function:
> 
>   int veprintf(int level, int var, const char *fmt, va_list args)
>   {
>           int ret = 0;
> 
>           if (var >= level) {
>                   if (use_browser >= 1 && redirect_to_stderr <= 0) {
>                           ui_helpline__vshow(fmt, args);
>                   } else {
>                           ret = fprintf_time(debug_file);
>                           ret += vfprintf(debug_file, fmt, args);
>                   }
>           }
> 
>           return ret;
>   }
> 
> If use quiet mode, verbose sets to -1. (also assigned in the perf_quiet_option function)
> Because "var >= level" is false, veprintf function returns directly, which avoids this problem.
> 
> However, there are cases where:
>   # perf --debug stderr=-1 report -vvv 2>/tmp/debug
> 
> If stderr is -1, should we redirect pr_debug in this case?

tools/perf/Documentation/perf.txt says debug variables are in value
range (0, 10), so -1 is invalid anyway.

> 
> Because I'm not sure if this is a problem,
> if redirect_to_stderr needs to be fixed as well,
> let me know and I'll submit a patch to fix it.

perf_quiet_option() sets redirect_to_stderr = -1 with the intention
that it turns it off, but it doesn't, although it gets turned of by
verbose = -1. Perhaps set redirect_to_stderr = 0 in perf_quiet_option() ?

I see we have another problem as well: places that check "if (verbose)"
instead of "if (verbose > 0)"

> 
>>
>>> and display_attr incorrectly determines the value of debug_peo_args.
>>> As a result, unexpected information is displayed.
>>>
>>> Before:
>>>    # perf record --quiet -- ls > /dev/null
>>>    ------------------------------------------------------------
>>>    perf_event_attr:
>>>      size                             128
>>>      { sample_period, sample_freq }   4000
>>>      sample_type                      IP|TID|TIME|PERIOD
>>>      read_format                      ID|LOST
>>>      disabled                         1
>>>      inherit                          1
>>>      mmap                             1
>>>      comm                             1
>>>      freq                             1
>>>      enable_on_exec                   1
>>>      task                             1
>>>      precise_ip                       3
>>>      sample_id_all                    1
>>>      exclude_guest                    1
>>>      mmap2                            1
>>>      comm_exec                        1
>>>      ksymbol                          1
>>>      bpf_event                        1
>>>    ------------------------------------------------------------
>>>    ...
>>>
>>> After:
>>>    # perf record --quiet -- ls > /dev/null
>>>    #
>>>
>>> Fixes: ccd26741f5e6 ("perf tool: Provide an option to print perf_event_open args and return value")
>>> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
>>
>> Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>
>>
> Thanks for reviewed-by.
> 
> Thanks,
> Yang