AF_VSOCK stream receives never fill msghdr.msg_inq. io_uring initialises the hint to -1 and treats that as "unknown", so it cannot set IORING_CQE_F_SOCK_NONEMPTY, and it speculatively retries a multishot receive after every completion, including when the queue is already empty.
Patch 1 fills the hint at the common exit of __vsock_connectible_recvmsg(), reusing vsock_stream_has_data(), the transport callback that SIOCINQ already uses. Following tcp_inq_hint(), it reports a terminal hint of 1 once the connection is finished, so the caller still performs the receive that observes EOF. Patch 2 adds selftest coverage. Numbers come from a ping-pong over vsock loopback using io_uring multishot receive, 4 KiB messages, the queue drained between messages, with kernel receives counted by a kprobe. The baseline is the same tree with patch 1 reverted: entries per delivered message 1.97 -> 1.00 (5000 messages) receiver CPU time, median 1.640s -> 1.587s (-3.2%) receiver wall time, median 3.260s -> 3.183s (-2.4%) Timing is 25 runs of 50000 messages per kernel; CPU gives Mann-Whitney p=0.006, wall time does not separate from noise (p=0.12), as expected for a latency-bound workload. The hint is gated to SOCK_STREAM; seqpacket is untouched. SO_INQ and SCM_INQ are deliberately left out: they need their own per-socket state and ancillary-message semantics, and a byte-count contract would have to account for transports reporting less than the whole queue. That can follow. Testing: built and run under virtme-ng on loopback, where the new cases pass and vsock_test still passes 41 of 41 with a clean dmesg. Other transports were reviewed but not tested. Hyper-V reports the current packet rather than the whole queue and can return -EIO; an undercount only understates what is readable, and a negative result leaves the caller's hint untouched. David Carlier (2): vsock: report pending receive data to io_uring vsock/test: cover receive queue hints net/vmw_vsock/af_vsock.c | 39 +++ tools/testing/vsock/vsock_uring_test.c | 367 +++++++++++++++++++++++++ 2 files changed, 406 insertions(+) base-commit: cea851523034d83dc61d882b1a6a3ad273480f7b -- 2.55.0
