On 02/26/2016 09:42 AM, Jason Wang wrote:
> This patch tries to poll for new added tx buffer or socket receive
> queue for a while at the end of tx/rx processing. The maximum time
> spent on polling were specified through a new kind of vring ioctl.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> drivers/vhost/net.c | 79 +++++++++++++++++++++++++++++++++++++++++++---
> drivers/vhost/vhost.c | 14 ++++++++
> drivers/vhost/vhost.h | 1 +
> include/uapi/linux/vhost.h | 6 ++++
> 4 files changed, 95 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 9eda69e..c91af93 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -287,6 +287,44 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
> rcu_read_unlock_bh();
> }
>
> +static inline unsigned long busy_clock(void)
> +{
> + return local_clock() >> 10;
> +}
> +
> +static bool vhost_can_busy_poll(struct vhost_dev *dev,
> + unsigned long endtime)
> +{
> + return likely(!need_resched()) &&
> + likely(!time_after(busy_clock(), endtime)) &&
> + likely(!signal_pending(current)) &&
> + !vhost_has_work(dev) &&
> + single_task_running();
> +}
> +
> +static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> + struct vhost_virtqueue *vq,
> + struct iovec iov[], unsigned int iov_size,
> + unsigned int *out_num, unsigned int *in_num)
> +{
> + unsigned long uninitialized_var(endtime);
> + int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
> + out_num, in_num, NULL, NULL);
> +
> + if (r == vq->num && vq->busyloop_timeout) {
> + preempt_disable();
> + endtime = busy_clock() + vq->busyloop_timeout;
> + while (vhost_can_busy_poll(vq->dev, endtime) &&
> + vhost_vq_avail_empty(vq->dev, vq))
> + cpu_relax();
Can you use cpu_relax_lowlatency (which should be the same as cpu_relax for almost
everybody but s390? cpu_relax (without low latency might give up the time slice
when running under another hypervisor (like LPAR on s390), which might not be what
we want here.
[...]
> +static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
> +{
> + struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
> + struct vhost_virtqueue *vq = &nvq->vq;
> + unsigned long uninitialized_var(endtime);
> + int len = peek_head_len(sk);
> +
> + if (!len && vq->busyloop_timeout) {
> + /* Both tx vq and rx socket were polled here */
> + mutex_lock(&vq->mutex);
> + vhost_disable_notify(&net->dev, vq);
> +
> + preempt_disable();
> + endtime = busy_clock() + vq->busyloop_timeout;
> +
> + while (vhost_can_busy_poll(&net->dev, endtime) &&
> + skb_queue_empty(&sk->sk_receive_queue) &&
> + vhost_vq_avail_empty(&net->dev, vq))
> + cpu_relax();
here as well.
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