linux-kernel - Re: iTCO_wdt watchdog on Asus P10S-WS motherboard FREEZES MOTHERBOARD COMPLETELY

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Date:   Wed, 21 Sep 2016 10:24:16 -0300
From:   Henrique de Moraes Holschuh <hmh@....eng.br>
To:     David Madore <david+ml@...ore.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linux Kernel mailing-list <linux-kernel@...r.kernel.org>
Subject: Re: iTCO_wdt watchdog on Asus P10S-WS motherboard FREEZES
 MOTHERBOARD COMPLETELY

On Wed, 21 Sep 2016, David Madore wrote:
> On Tue, Sep 20, 2016 at 03:50:09PM +0300, Mika Westerberg wrote:
> > Does the machine have WDAT ACPI table (see /sys/firmware/acpi/tables/*)?
> > If it does, you can try the new WDAT watchdog driver instead [1]. It
> > still uses the same hardware, though but via set of instructions
> > provided by the BIOS that should work (given the vendor has tested
> > it on Windows).
> > 
> > [1] http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1230607.html
> 
> Thanks for pointing this out.  My motherboard's BIOS does not have
> this ACPI table, unfortunately, but it's at least good to know that
> some do, and take the hardware watchdog seriously.

The ones that take the hardware watchdog seriously will command the
power supply to do a power cycle when it triggers, which pretty much
cuts power to everything that is not hanging off the +5VSB (standby
power) line.

Let's just say that SSDs don't like it, at all.  Avoid at *all* *costs*.

I have been using the kernel's software watchdog on most systems because
of that: it just soft-reboots, which is good enough almost every time
and doesn't mess with the SSDs.

The proper fix is to have two levels of watchdogs, a soft reboot on time
T for the first level, and a power cycle on time 5T (to give the BIOS
enough of a time window to reset the second level watchdog during a soft
reboot).

-- 
  Henrique Holschuh