Re: [PATCH 1/2] x86_64 nmi_watchdog: Make check_nmi_watchdog static

[ebiederm@xmission.com (Eric W. Biederman)]

Andi Kleen <ak@suse.de> writes:

> On Tuesday 04 October 2005 17:26, Eric W. Biederman wrote:
>> Andi Kleen <ak@suse.de> writes:
>> > On Tuesday 04 October 2005 17:11, Eric W. Biederman wrote:
>> >> By using a late_initcall as i386 does we don't need to call
>> >> check_nmi_watchdog manually after SMP startup, and we don't
>> >> need different code paths for SMP and non SMP.
>> >>
>> >> This paves the way for moving apic initialization into init_IRQ,
>> >> where it belongs.
>> >
>> > I don't like it. I want to see a clear message in the log when
>> > the NMI watchdog doesn't work and with your patch that comes too late.
>>
>> Why is it to late?
>
> It's after too much of the boot. e.g. consider analyzing log with a boot hang.
> It's important to know if the NMI watchdog runs or not. For that it is
> best when the test of it happens as early as possible.

That make sense.

>> > -Andi (who has rejected similar patches before)
>>
>> Would it be more appropriate to make this a per cpu check?
>
> That would be fine as long as it's as early as possible.
> But I suspect you'll always need special cases for the BP
> because it needs the timer running first.

Well a special call site certainly but I can probably get away
with a single function called from the appropriate CPU.  I
might even be able to remove nmi_cpu_busy :)

It will take me a bit to get my head back into that part of the
code.  late_initcall was a nice solution from a correctness
and simplicity point of view.  But obviously it had other issues :)

There is the whole late_timer_init() which is probably where
the test needs to happen for the boot processor.

Eric