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

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Date:   Sat, 11 Feb 2017 21:41:33 +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:

> On Sat, Feb 11, 2017 at 06:59:10PM +0100, Ingo Molnar wrote:
> > So I checked the perf-list manpage and it didn't tell me much about how to disable 
> > the NMI watchdog.
> 
> Oh, it is buried there:
> 
> "
> EVENT GROUPS
> ------------
> 
> ...
> 
> 
> Globally pinned events can limit the number of counters available for
> other groups. On x86 systems, the NMI watchdog pins a counter by default.
> The nmi watchdog can be disabled as root with
> 
> 	echo 0 > /proc/sys/kernel/nmi_watchdog"
> 
> > How about a more proactive hint, something like:
> > 
> > 	To disable the NMI watchdog permanently, do:
> 
> Why permanently? We want it to run and be disabled around the
> measurement only. Anyway, here's something more to the point:

> +	if (print_free_counters_hint)
> +		fprintf(output,
> +"Some events weren't counted. Try disabling the NMI watchdog:\n"
> +"	echo 0 > /proc/sys/kernel/nmi_watchdog\n"
> +"	perf stat ...\n"
> +"	echo 1 > /proc/sys/kernel/nmi_watchdog\n");
>  }

Ok, looks good to me!

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo