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Re: MI non-interlocked atomic ops?
> David Young <dyoung%pobox.com@localhost> wrote:
>> which spends (on x86) a small but not immeasurable amount of time in
>> splx(s), so I was tempted to rewrite it like this:
>> mbstat_type_add(int type, int diff)
>> struct mbstat_cpu *mb;
>> mb = percpu_getref(mbstat_percpu);
>> atomic_add_uint_ni(&mb->m_mtypes[type], diff);
>> There is no such routine as atomic_add_uint_ni(), though, and I don't
>> know if every NetBSD architecture can supply that routine.
> Right, spl*()/splx() have a cost. However, code like this (networking)
> should not be in the hard-interrupt handler. As we move towards a wider
> use of software interrupts, SPL calls will disappear and kernel preemption
> provides the necessary protection (although software interrupts are not
> yet preemptable).
iirc kpreempt_disable() doesn't provide a protection from a softint.
> We have non-interlocked CAS operation - atomic_cas_*_ni(). This can be
> used to replicate all other operations. I doubt there is much need to
> define them all due to the reason stated above. CAS is enough for now.
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