Thank you very much for the detailed answer! So I think I will more safely build on top of liburing! Lorenzo Il giorno mer 6 mag 2020 alle ore 15:45 Pavel Begunkov <asml.silence@xxxxxxxxx> ha scritto: > > 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
