Re: [PATCH V3 3/3] vhost_net: basic polling support
From: Christian Borntraeger <hidden>
Date: 2016-02-28 21:57:00
Also in:
kvm, lkml, netdev
On 02/26/2016 09:42 AM, Jason Wang wrote:
quoted hunk ↗ jump to hunk
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@redhat.com> --- 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.