Hello, I have been recently working on a library that implements futex wait-queues in user-space (see https://sstewartgallus.com/git?p=uevents.git;a=summary .) The basic idea is that an event semaphore is implemented by a queue of "notifiers" that waiters and signallers enqueue and dequeue to and from. Each notifier could be implemented in a multitude of ways such as eventfds, pipes, spinning on a memory location or futexes. However, while I found my implementation has several possible performance advantages I also found that it has trouble properly implementing thread priorities when used to implement locks. One could easily extend my implementation by making each event semaphore have 40 queues (one for each priority) but properly implementing priority inheritance seems to be difficult. Because each waiter waits on a separate notifier it seems to me that to properly implement priority inheritance with futexes I'd have to iterate over all notifiers on the queue and set their wait location to the PID of the thread that has currently acquired the lock. Anyway, I thought it was an interesting problem dealing with low-level futex stuff that linux-smp might be interested in. Thank you, Steven Stewart-Gallus -- To unsubscribe from this list: send the line "unsubscribe linux-smp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
