On 26-Feb-02 Bruce Evans wrote:
> On Tue, 26 Feb 2002, John Baldwin wrote:
>> The critical section stuff currently in current is part of the original
>> preemption patches I wrote at Usenix last year.  They aren't in the tree
>> because they aren't stable yet.  We still have problems on the alpha and
>> problems with IPI deadlocks on SMP machines that need to be worked out. 
>> Since
>> this API is still very much in flux I'd prefer to keep it simple for now and
>> not make the code overly complex with optimizations until after we have
>> settled
>> on the design.
> The change is mostly part of the design change needed to un-break fast
> interrupt handlers.  critical_enter() mask not mask hardware
> interrupts for the same reason than splhigh() must not mask them:
> there is too much MI code that thinks it is critical and short but
> really isn't (e.g., everything under spinlocks in -current).  Changing
> cpu_critical_enter() to a null version to prevent spinlocks masking
> interrupts doesn't work very well because it is used for other things
> that really do need to mask interrupts.  Having 2 levels for
> cpu_critical_enter() (on that masks normal interrupts and one that
> masks fast interrupts) would work but I think there are already too
> many levels of critical_enter()s.

I think having the sparc-like API of intr_disable() / intr_restore() that we
used to use to fix the places that assume too many implementation details of
cpu_critical_foo() would be a good first step so that cpu_critical_foo() can be
relegated back to supporting non-preemption (and no other spinlocks) and
nothing else.

> Bruce


John Baldwin <[EMAIL PROTECTED]>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/

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