* Greg Lehey <gr...@lemis.com> [000703 16:10] wrote:

The idea is that for spin or spin-then-sleep mutexes (very short hold time) is that since you won't have as many processes as cpus contending (and when you do it's ok) that the mutual exclusion is so short lived that by the time the next 'thundering' process is actually given the CPU, the likelyhood is that other processes have already aquired _and_ released the spinlock making it more than likely that the reasource is free.

The idea is that the a quantum is actually so great that there's little chance of one of the wake_all processes colliding on the lock.

By effectively you gain a whole lot because you avoid having to grab sched-mutex on each aquire/release and you also reduce the cache cost of wakeups because it's likely that only once kernel context will wind its way down the sleep queue.

What sort of interesting is that doing it one way or the other is so similar that in reality the initial implementation doesn't matter, switching from one to the other will be trivial at most, the importance lies in getting one implementation done.

-Alfred

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