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SubjectRe: [PATCH RFC 1/4] vsock/virtio: reduce credit update messages
On Thu, Apr 04, 2019 at 12:58:35PM +0200, Stefano Garzarella wrote:
> @@ -256,6 +257,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> struct virtio_vsock_sock *vvs = vsk->trans;
> struct virtio_vsock_pkt *pkt;
> size_t bytes, total = 0;
> + s64 free_space;

Why s64? buf_alloc, fwd_cnt, and last_fwd_cnt are all u32. fwd_cnt -
last_fwd_cnt <= buf_alloc is always true.

> int err = -EFAULT;
>
> spin_lock_bh(&vvs->rx_lock);
> @@ -288,9 +290,15 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> }
> spin_unlock_bh(&vvs->rx_lock);
>
> - /* Send a credit pkt to peer */
> - virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
> - NULL);
> + /* We send a credit update only when the space available seen
> + * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE
> + */
> + free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);

Locking? These fields should be accessed under tx_lock.

> + if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
> + virtio_transport_send_credit_update(vsk,
> + VIRTIO_VSOCK_TYPE_STREAM,
> + NULL);
> + }
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