linux-kernel - Re: [RFC PATCH] perf/stat: Add --disable-hwdt

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Date:   Sat, 11 Feb 2017 18:59:10 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Robert Richter <rric@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vince Weaver <vince@...ter.net>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] perf/stat: Add --disable-hwdt


* Borislav Petkov <bp@...en8.de> wrote:

> Ok,
> 
> turns out perf-list(1) already talks about it in the "EVENT GROUPS"
> section. How about this then:
> 
> ---
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index a02f2e965628..2d18283574db 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -146,6 +146,7 @@ static aggr_get_id_t		aggr_get_id;
>  static bool			append_file;
>  static const char		*output_name;
>  static int			output_fd;
> +static int			print_free_counters_hint;
>  
>  struct perf_stat {
>  	bool			 record;
> @@ -1109,6 +1110,9 @@ static void printout(int id, int nr, struct perf_evsel *counter, double uval,
>  			counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED,
>  			csv_sep);
>  
> +		if (counter->supported)
> +			print_free_counters_hint = 1;
> +
>  		fprintf(stat_config.output, "%-*s%s",
>  			csv_output ? 0 : unit_width,
>  			counter->unit, csv_sep);
> @@ -1476,7 +1480,13 @@ static void print_footer(void)
>  		print_noise_pct(stddev_stats(&walltime_nsecs_stats),
>  				avg_stats(&walltime_nsecs_stats));
>  	}
> +
>  	fprintf(output, "\n\n");
> +
> +	if (print_free_counters_hint)
> +		fprintf(output,
> +"Some events couldn't be scheduled. Consider freeing some counters by disabling the NMI watchdog temporarily, \n"
> +"for example. See perf-list(1) manpage.\n");

So I checked the perf-list manpage and it didn't tell me much about how to disable 
the NMI watchdog.

How about a more proactive hint, something like:

	To disable the NMI watchdog permanently, do:

		sudo echo kernel.nmi_watchdog=0 >> /etc/sysctl.conf
		sudo sysctl -p

? (untested!)

Thanks,

	Ingo