linux-kernel - Re: [PATCH] perf intel-pt: Fix error with config term pt=0

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Date:   Tue, 27 Nov 2018 09:39:28 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf intel-pt: Fix error with config term pt=0

Em Tue, Nov 27, 2018 at 10:43:36AM +0200, Adrian Hunter escreveu:
> Users should never use 'pt=0', but if they do it may give a meaningless
> error:
> 
> 	$ perf record -e intel_pt/pt=0/u uname
> 	Error:
> 	The sys_perf_event_open() syscall returned with 22 (Invalid argument) for
> 	event (intel_pt/pt=0/u).
> 
> Fix that by forcing 'pt=1'.
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/arch/x86/util/intel-pt.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
> index db0ba8caf5a2..af25a7824ee0 100644
> --- a/tools/perf/arch/x86/util/intel-pt.c
> +++ b/tools/perf/arch/x86/util/intel-pt.c
> @@ -524,10 +524,18 @@ static int intel_pt_validate_config(struct perf_pmu *intel_pt_pmu,
>  				    struct perf_evsel *evsel)
>  {
>  	int err;
> +	char c;
>  
>  	if (!evsel)
>  		return 0;
>  
> +	/*
> +	 * If supported, force pass-through config term (pt=1) even if user
> +	 * sets pt=0, which avoids senseless kernel errors.
> +	 */
> +	if (perf_pmu__scan_file(intel_pt_pmu, "format/pt", "%c", &c) == 1)
> +		evsel->attr.config |= 1;

shouldn't we have a warning like:

   pr_warning("pt=0 doesn't make sense, forcing pt=1")


Instead of silently doing something the user, mistakenly, did
explicitely?

- Arnaldo
  

> +
>  	err = intel_pt_val_config_term(intel_pt_pmu, "caps/cycle_thresholds",
>  				       "cyc_thresh", "caps/psb_cyc",
>  				       evsel->attr.config);
> -- 
> 2.17.1

-- 

- Arnaldo