[Xenomai] perf nmi on x86

[Xenomai] perf nmi on x86

[Gilles Chanteperdrix]

Hi Jan,

running Xenomai on an x86 machine, I noticed that the perf NMI was
ticking. It seems CONFIG_PERF can not be disabled in the kernel
configuration.

So, the first question is: 
is there a way of disabling the NMI ?
second question is: 
if not, what do we do about it? 

I mean, on the one hand, disabling the NMI is probably mandatory on
a system where latency matters, but on the other hand, some users
may want it enabled and do not care for the additional latency.

Regards.

-- 
					    Gilles.
https://click-hack.org

Re: [Xenomai] perf nmi on x86

[Jan Kiszka]

On 2015-08-24 20:14, Gilles Chanteperdrix wrote:
> Hi Jan,
> 
> running Xenomai on an x86 machine, I noticed that the perf NMI was
> ticking. It seems CONFIG_PERF can not be disabled in the kernel
> configuration.
> 
> So, the first question is: 
> is there a way of disabling the NMI ?
> second question is: 
> if not, what do we do about it? 
> 
> I mean, on the one hand, disabling the NMI is probably mandatory on
> a system where latency matters, but on the other hand, some users
> may want it enabled and do not care for the additional latency.

Does "echo 0 > /proc/sys/kernel/nmi_watchdog" change the picture? It did
so for me on a distro kernel, though re-enabling it again didn't make
the PMIs reappear.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux

Re: [Xenomai] perf nmi on x86

[Gilles Chanteperdrix]

On Mon, Aug 24, 2015 at 08:24:17PM +0200, Jan Kiszka wrote:
> On 2015-08-24 20:14, Gilles Chanteperdrix wrote:
> > Hi Jan,
> > 
> > running Xenomai on an x86 machine, I noticed that the perf NMI was
> > ticking. It seems CONFIG_PERF can not be disabled in the kernel
> > configuration.
> > 
> > So, the first question is: 
> > is there a way of disabling the NMI ?
> > second question is: 
> > if not, what do we do about it? 
> > 
> > I mean, on the one hand, disabling the NMI is probably mandatory on
> > a system where latency matters, but on the other hand, some users
> > may want it enabled and do not care for the additional latency.
> 
> Does "echo 0 > /proc/sys/kernel/nmi_watchdog" change the picture? It did
> so for me on a distro kernel, though re-enabling it again didn't make
> the PMIs reappear.

Works for me, and writing 1 seems to re-enable it. Thanks. This
should really be documented somewhere, though.

-- 
					    Gilles.
https://click-hack.org