diff options
authorJens Axboe <>2022-04-16 07:38:19 -0600
committerJens Axboe <>2022-04-16 07:38:19 -0600
commit8b205b8b82104589b869364bc11e1d9156be8dfa (patch)
parent7983bed070cbea274edc6224d7fb2137c82e3854 (diff)
man/io_uring_register.2: clarify eventfd notification counts
We may see both spurious eventfd notifications (eg an eventfd notification was posted, yet no CQEs are available), as well as batched notifications where a batch of CQEs are posted but only a single eventfd notification generated. Signed-off-by: Jens Axboe <>
1 files changed, 7 insertions, 1 deletions
diff --git a/man/io_uring_register.2 b/man/io_uring_register.2
index cb63e6b..1e91caf 100644
--- a/man/io_uring_register.2
+++ b/man/io_uring_register.2
@@ -328,7 +328,13 @@ registered through this operation.
.I arg
must contain a pointer to the eventfd file descriptor, and
.I nr_args
-must be 1. Available since 5.2.
+must be 1. Note that while io_uring generally takes care to avoid spurious
+events, they can occur. Similarly, batched completions of CQEs may only trigger
+a single eventfd notification even if multiple CQEs are posted. The application
+should make no assumptions on number of events being available having a direct
+correlation to eventfd notifications posted. An eventfd notification must thus
+only be treated as a hint to check the CQ ring for completions. Available since
An application can temporarily disable notifications, coming through the
registered eventfd, by setting the