Proof of concept for io_uring futex requests. The wake side does FUTEX_WAKE_OP type of modify-compare operation but with a single address. Wait reqs go through io-wq and so slow path. Should be interesting for a bunch of people, so we should first outline API and capabilities it should give. As I almost never had to deal with futexes myself, would especially love to hear use case, what might be lacking and other blind spots. 1) Do we need PI? 2) Do we need requeue? Anything else? 3) How hot waits are? May be done fully async avoiding io-wq, but apparently requires more changes in futex code. 4) We can avoid all page locking/unlocking for shared futexes with pre-registration. How much is it interesting? For _very_ basic examples see [1] [1] https://github.com/isilence/liburing/tree/futex_v1 Pavel Begunkov (4): futex: add op wake for a single key io_uring: frame out futex op io_uring: support futex wake requests io_uring: implement futex wait fs/io_uring.c | 91 +++++++++++++++++++++++++++++++++++ include/linux/futex.h | 15 ++++++ include/uapi/linux/io_uring.h | 19 +++++++- kernel/futex.c | 64 +++++++++++++++++++++++- 4 files changed, 186 insertions(+), 3 deletions(-) -- 2.31.1
