On 04/05/2020 19:54, Lorenzo Gabriele wrote: > Hi everyone, > I'm a complete noob so sorry if I'm saying something stupid. > I want to have a liburing-like library for the Scala Native language. > I can't easily use liburing itself because of some limitations of the > language.. So I was rewriting the C code in liburing in Scala Native. > The language is single threaded and, sadly, doesn't support atomic, > nor volatile. I was thinking what are the implications of completely > removing the memory barriers. > Are they needed for something related with multithreading or they are > needed regardless to utilize io_uring? Long story short, even if your app is single-threaded, io_uring is _not_. I wouldn't recommend removing it. See the comment below picked from io_uring.h /* * After the application reads the CQ ring tail, it must use an * appropriate smp_rmb() to pair with the smp_wmb() the kernel uses * before writing the tail (using smp_load_acquire to read the tail will * do). It also needs a smp_mb() before updating CQ head (ordering the * entry load(s) with the head store), pairing with an implicit barrier * through a control-dependency in io_get_cqring (smp_store_release to * store head will do). Failure to do so could lead to reading invalid * CQ entries. */ More difficult to say, what will actually happen. E.g. if you don't use polling io_uring modes, and if you don't do speculative CQ reaping, there is a pairing smp_rmb() just before returning from a wait. But, again, the io_uring ABI doesn't guarantee correctness without them. -- Pavel Begunkov
