In non-busypoll handle_rx paths, if peek_head_len returns 0, the RX loop breaks, the RX wait queue is re-enabled, and vhost_net_signal_used is called to flush done_idx and notify the guest if needed.
However, signaling the guest can take non-trivial time. During this window, additional RX payloads may arrive on rx_ring without further kicks. These new payloads will sit unprocessed until another kick arrives, increasing latency. In high-rate UDP RX workloads, this was observed to occur over 20k times per second. To minimize this window and improve opportunities to process packets promptly, immediately call peek_head_len after signaling. If new packets are found, treat it as a busy poll interrupt and requeue handle_rx, improving fairness to TX handlers and other pending CPU work. This also helps suppress unnecessary thread wakeups, reducing waker CPU demand. Signed-off-by: Jon Kohler <[email protected]> --- drivers/vhost/net.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 35ded4330431..04cb5f1dc6e4 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -1015,6 +1015,27 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk, struct vhost_virtqueue *tvq = &tnvq->vq; int len = peek_head_len(rnvq, sk); + if (!len && rnvq->done_idx) { + /* When idle, flush signal first, which can take some + * time for ring management and guest notification. + * Afterwards, check one last time for work, as the ring + * may have received new work during the notification + * window. + */ + vhost_net_signal_used(rnvq, *count); + *count = 0; + if (peek_head_len(rnvq, sk)) { + /* More work came in during the notification + * window. To be fair to the TX handler and other + * potentially pending work items, pretend like + * this was a busy poll interruption so that + * the RX handler will be rescheduled and try + * again. + */ + *busyloop_intr = true; + } + } + if (!len && rvq->busyloop_timeout) { /* Flush batched heads first */ vhost_net_signal_used(rnvq, *count); -- 2.43.0
