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

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Date:   Wed, 28 Nov 2018 10:09:42 -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 Wed, Nov 28, 2018 at 02:38:13PM +0200, Adrian Hunter escreveu:
> On 27/11/18 2:39 PM, Arnaldo Carvalho de Melo wrote:
> > 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?
> 
> Sure, here it is:

Thanks, sticked this to the cset:

------------------------

Committer testing:

  # 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).
  /bin/dmesg | grep -i perf may provide additional information.

  # perf record -e intel_pt/pt=0/u uname
  pt=0 doesn't make sense, forcing pt=1
  Linux
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.020 MB perf.data ]
  #
------------------------

Thanks, applied.

- Arnaldo