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SubjectRe: [PATCH 7/9] watchdog: enable the new user interface of the watchdog mechanism
On Mon, Feb 23, 2015 at 01:19:46PM -0800, Andrew Morton wrote:
> On Thu, 5 Feb 2015 15:40:23 -0500 Don Zickus <dzickus@redhat.com> wrote:
>
> > From: Ulrich Obergfell <uobergfe@redhat.com>
> >
> > With the current user interface of the watchdog mechanism it is only
> > possible to disable or enable both lockup detectors at the same time.
> > This series introduces new kernel parameters and changes the semantics
> > of some existing kernel parameters, so that the hard lockup detector
> > and the soft lockup detector can be disabled or enabled individually.
> > With this series applied, the user interface is as follows.
> >
> > - parameters in /proc/sys/kernel
> >
> > . soft_watchdog
> > This is a new parameter to control and examine the run state of
> > the soft lockup detector.
> >
> > . nmi_watchdog
> > The semantics of this parameter have changed. It can now be used
> > to control and examine the run state of the hard lockup detector.
> >
> > . watchdog
> > This parameter is still available to control the run state of both
> > lockup detectors at the same time. If this parameter is examined,
> > it shows the logical OR of soft_watchdog and nmi_watchdog.
> >
> > . watchdog_thresh
> > The semantics of this parameter are not affected by the patch.
> >
> > - kernel command line parameters
> >
> > . nosoftlockup
> > The semantics of this parameter have changed. It can now be used
> > to disable the soft lockup detector at boot time.
> >
> > . nmi_watchdog=0 or nmi_watchdog=1
> > Disable or enable the hard lockup detector at boot time. The patch
> > introduces '=1' as a new option.
> >
> > . nowatchdog
> > The semantics of this parameter are not affected by the patch. It
> > is still available to disable both lockup detectors at boot time.
>
> So we need a whole bunch of updates and additions to Documentation/?

Ok.

>
> Are all these changes back-compatible with previous kernel versions?

I believe so. The motivation for some of the change was the ambiguity of
the /proc/sys/kerne/watchdog variable. This patchset clears that up. So
if it breaks backward compatibility, it is because it was misinterpreted
from its original intention.

Old definition of the proc/sys/kernel variable:

watchdog == nmi_watchdog_enabled

New definition:

watchdog == nmi_watchdog_enabled | softlockup_enabled


Cheers,
Don

>
>


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