svn commit: r213985 - head/sys/sparc64/sparc64

[Alexander Motin]

Marius Strobl wrote:
> On Mon, Oct 18, 2010 at 05:05:24PM -0400, John Baldwin wrote:
>> On Monday, October 18, 2010 4:52:24 pm Marius Strobl wrote:
>>> AFAICT this is not true; intr_event_handle() in sys/kern/kern_intr.c
>>> is what enters a critical section and f.e. on amd64 I don't see where
>>> anywhere in the path from ISR_VEC() to intr_execute_handlers()
>>> calling intr_event_handle() a critical section would be entered,
>>> which also means that in intr_execute_handlers() td_intr_nesting_level
>>> is incremented outside of a critical section.
>> Not all of the clock interrupts use intr_event_handle().  The local APIC
>> timer uses its own interrupt entry point on x86 for example and uses an
>> explicit critical section as a result.  I suspect the sparc64 tick interrupt
>> is closer to the local APIC timer case and doesn't use intr_event_handle().
> 
> Correct; but still you can't say that the MD interrupt code enters a
> critical section in general, neither is incrementing td_intr_nesting_level
> in intr_execute_handlers() protected by a critical section.
> 
>> The fact that some clock interrupts do use intr_event_handle() (e.g. the
>> atrtc driver on x86 now) does indicate that the low-level interrupt code
>> probably does not belong in the time events code but in the caller.
> 
> Well, I agree that entering a critical section in the time events
> code would mean entering a nested critical section unnecessarily in
> case the clock driver uses a regular "fast" interrupt handler and
> that should be avoided. Still I don't think the event time front-end
> actually should need to worry about wrapping the callback in a
> critical section.

Interrupt frame, required for hard-/stat-/profclock() operation is
stored in curthread. So critical section is effectively mandatory there
now. Correct td_intr_nesting_level value is also important for proper
interrupt threads scheduling - one more reason to have critical section
there. It is indeed strange that td_intr_nesting_level in
intr_event_handle() is not covered by critical section, but probably it
should.

-- 
Alexander Motin