Hi, We never supported provided buffers for sends, because it didn't seem to make a lot of sense. But it actually does make a lot of sense! If an app is receiving data, doing something with it, and then sending either the same or another buffer out based on that, then if we use provided buffers for sends we can guarantee that the sends are serialized. This is because provided buffer rings are FIFO ordered, as it's a ring buffer, and hence it doesn't really matter if you have more than one send inflight. This provides a nice efficiency win, but more importantly, it reduces the complexity in the application as it no longer needs to track a potential backlog of sends. The app just sets up a send based buffer ring, exactly like it does for incoming data. And that's it, no more dealing with serialized sends. In some testing with proxy [1], in basic shuffling of packets I see a 36% improvement with this over manually dealing with sends. That's a pretty big win on top of making the app simpler. This also opens the door for multishot send requests, which is an interesting future venue to pursue! You can also find the patches here: https://git.kernel.dk/cgit/linux/log/?h=io_uring-send-queue [1] https://git.kernel.dk/cgit/liburing/tree/examples/proxy.c -- Jens Axboe
