Re: [RFC 1/3] Unified NMI delayed call mechanism

Ingo Molnar
2010-06-18T09:48:54Z

* Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> wrote:

> (2010/06/12 19:25), Ingo Molnar wrote:
> >
> > * Huang Ying <ying.huang@intel.com> wrote:
> >
> >> NMI can be triggered even when IRQ is masked. So it is not safe for NMI
> >> handler to call some functions. One solution is to delay the call via self
> >> interrupt, so that the delayed call can be done once the interrupt is
> >> enabled again. This has been implemented in MCE and perf event. This patch
> >> provides a unified version and make it easier for other NMI semantic handler
> >> to take use of the delayed call.
> >
> > Instead of introducing this extra intermediate facility please use the same
> > approach the unified NMI watchdog is using (see latest -tip): a perf event
> > callback gives all the extra functionality needed.
> >
> > The MCE code needs to be updated to use that - and then it will be integrated
> > into the events framework.
>
> Hi Ingo,
>
> I think this "NMI delayed call mechanism" could be a part of "the events
> framework" that we are planning to get in kernel soon. [...]

My request was to make it part of perf events - which is a generic event
logging framework. We dont really need/want a second 'events framework'
as we have one already ;-)

> [...] At least APEI will use NMI to report some hardware events (likely
> error) to kernel. So I suppose we will go to have a delayed call as an
> event handler for APEI.

Yep, that makes sense. I wasnt arguing against the functionality itself, i was
arguing against the illogical layering that limits its utility. By making it
part of perf events it becomes a generic part of that framework and can be
used by anything that deals with events and uses that framework.

Thanks,

Ingo