Hi, Normal CQE waiting is generally either done with a timeout, or without one. Outside of the timeout, the other key parameter is how many events to wait for. If we ask for N events and we get that within the timeout, then we return successfully. If we do not, then we return with -ETIME and the application can then check how many CQEs are actually available, if any. This works fine, but we're increasingly using smaller timeouts in applications for targeted batch waiting. Eg "give me N requests in T usec". If the application has other things do do every T usec, this works fine. But if it's an event loop that wants to process completions to make progress, it's pointless to return after T usec if there's nothing to do. The application can't really make T bigger reliably, as this may be the target it has to meet at busier times of the day. This patchset adds support for min timeout waiting, which adds a third parameter to how waits are done. The N and T timeout remain, but we add a min_timeout option, M. The batch is now defined by N and M. The application can now say "give me N requests in M usec, but if none have arrived, just sleep until T has passed". This allows for using a sane N+M, while avoid waking and returning all the time if nothing happens. The semantics are as follows: - If M expires and no events are available, keep waiting until T has expired. This is identical to using N+T without setting M at all, except if an event arrives after M has expired, we return immediately. - If M expires and events are available, return those even if it's less than N. - If N events arrive before M expires, return those events. This is identical to T == M, and M not being set. There's a liburing branch with test cases here: https://git.kernel.dk/cgit/liburing/log/?h=min-wait and the patches are on top of the current for-6.9/io_uring branch. They can also be viewed here: https://git.kernel.dk/cgit/linux/log/?h=io_uring-min-wait include/uapi/linux/io_uring.h | 3 +- io_uring/io_uring.c | 156 ++++++++++++++++++++++++++++------ io_uring/io_uring.h | 4 + 3 files changed, 134 insertions(+), 29 deletions(-) Changes since v1: - Fix issue with both min_wait and timeout, and transitioning to the long timeout. We'd add the current time potentially more than once, causing much longer waits than what was asked for. Test case has been added for that as well. -- Jens Axboe
