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

Huang Ying
2010-06-13T01:54:12Z

On Sat, 2010-06-12 at 18:25 +0800, 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.
> >
> > Signed-off-by: Huang Ying <ying.huang@intel.com>
> > ---
> > arch/x86/include/asm/entry_arch.h | 1
> > arch/x86/include/asm/hw_irq.h | 1
> > arch/x86/include/asm/irq_vectors.h | 5 +
> > arch/x86/include/asm/nmi.h | 7 ++
> > arch/x86/kernel/entry_64.S | 3 +
> > arch/x86/kernel/irqinit.c | 3 +
> > arch/x86/kernel/traps.c | 104 +++++++++++++++++++++++++++++++++++++
> > 7 files changed, 124 insertions(+)
>
> 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.

Sorry, if my understanding is correct, the perf event overflow callback
should be run in NMI context instead of a delayed context (such as IRQ,
soft_irq, process context). That is, the backtrace of
watchdog_overflow_callback should be something as follow:

x86_pmu_handle_irq
perf_event_overflow
__perf_event_overflow
watchdog_overflow_callback

I do not find the delayed mechanism here.

> The MCE code needs to be updated to use that - and then it will be integrated
> into the events framework.

MCE is NMI-like, and there are other NMI users too. I think some of them
will need some kind of delayed call mechanism. In fact, perf itself uses
self-made NMI delayed call mechanism too, I just want to generalize it
for other users too.

Best Regards,
Huang Ying