I didn't intend to change the behavior of an existing blocking call with
adaptive spinning if that is what you are getting at here. Initially
there would be a new futex op, something like FUTEX_LOCK_ADAPTIVE or
maybe just FUTEX_WAIT_ADAPTIVE. Applications can use this directly to
implement adaptive spinlocks. Ideally glibc would make use of this via
either the existing adaptive spinning NP API or via a new one. Before we
even go there, we need to see if this can provide a real benefit.
Polled lock == userspace spinlock?
That's true with any userland lock.
Again, my intention is not to replace any existing functionality, so
applications would have to explicitly request this behavior.
If I'm missing your point, please elaborate.
IBM Linux Technology Center
Real-Time Linux Team