Luoqi Chen wrote:

Its basically for lock size, to keep the locks really small so each lock inside other structures wouldn't get too large. The cache line size doesn't matter so much as the size of the other structures that contain locks. But, if you make structures large (by including large locks in them) they won't fit in cache lines so well. In a fine-grained implementation, lots of small structures need locking.

You only need turnstiles for the locks that are being waited on, but the turnstile can't be in the thread (or process) that's doing the waiting. There are a lot more mutexes and r/w locks than there are potential waiters, so its a big waste of space to have all the data per lock.

The main thing is to not block on mutexes very frequently. The cost of blocking is secondary if the frequency is low enough.

There are a lot of considerations and a lot of trial-and-error involved in getting a balanced (not perfect) implementation.

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