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

From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Robert Richter <rric@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Vince Weaver <vince@deater.net>,
	lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] perf/stat: Add --disable-hwdt
Date: Sat, 11 Feb 2017 21:41:33 +0100	[thread overview]
Message-ID: <20170211204132.GB19264@gmail.com> (raw)
In-Reply-To: <20170211183218.ijnvb5f7ciyuunx4@pd.tnic>

* Borislav Petkov <bp@alien8.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@kernel.org>

Thanks,

	Ingo