Re: [Xen-devel] [PATCHv1] x86: only check for one watchdog NMI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.06.15 at 18:21, <david.vrabel@xxxxxxxxxx> wrote:
> Since the NMI handler can now recognize watchdog NMIs, make
> check_nmi_watchdog() only check for at least one watchdog NMI.  This
> prevents false negatives caused by other processors (which may be
> being power managed by the BIOS) running at reduced clock frequencies.

Doesn't this go a little too far, in that it allows through the case where
an NMI works exactly once (a behavior not unheard of)? Lowering the
count to e.g. 3 would seem acceptable, but not any further. Raising
the wait time might then need to be the way to go if the (approximate)
1:3 ratio still isn't enough to cope with BIOS power managed CPUs.

Btw., can an OS know of the power state CPUs come up in? I.e. can
the wait time be adjusted dynamically? Or is this (perhaps intentionally)
completely transparent to the OS?

Jan


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