Re: [patch] serial console vs NMI watchdog

george anzinger
2001-03-12T08:32:35Z

Keith Owens wrote:
>
> On Sun, 11 Mar 2001 20:43:16 -0800,
> george anzinger <george@mvista.com> wrote:
> >Consider this. Why not use the NMI to sync the cpus. Kdb would have a
> >function that is called each NMI.
>
> kdb uses NMI IPI to get the other cpu's attention. One cpu is in
> control and may or may not be accepting NMI, it depends on the event
> that entered kdb. The other cpus end up in kdb code, spinning waiting
> for a cpu switch. Initially they are not receiving NMI because they
> were invoked via NMI which is masked until they exit. However if the
> user does a cpu switch then single steps the interrupted code, the cpu
> has to return from the NMI handler to the interrupted code at which
> time this cpu starts receiving NMI again.

Are you actually twiddling the hardware, or just changing what happens
on NMI?
>
> The kdb context can change from ignoring NMI to accepting NMI. It is
> easier to bring all the cpus into kdb and let the kdb code decide if it
> ignores any NMI that is being received.

Yes. Exactly.

George