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SubjectRe: spinaphore conceptual draft (was discussion of RT patch)
One thing you are forgetting is that we are not just talking about the
latencies of contention. We are talking about the latency of a high
priority process when it wakes up to the time it runs. Most of the time
a spin lock stops preemption, either with (CONFIG_PREEMPT)
preempt_disable or simple turning off interrupts. With Ingo's mutexes,
the places with spin_locks are now preemptable. So there is probably
lots of times that it would be better to just spin on contention, but
that's not what Ingo's spin_locks are saving us. It's to keep most of
the kernel preemptable.

The priority inheritance of spin_locks is simply there to protect from
priority inversion.

-- Steve

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