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Date: Tue, 31 May 2016 11:14:10 +0800 From: Jason Wang <jasowang@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH V2 1/2] vhost_net: stop polling socket during rx processing On 2016年05月30日 23:47, Michael S. Tsirkin wrote: > On Mon, May 30, 2016 at 02:47:53AM -0400, Jason Wang wrote: >> We don't stop rx polling socket during rx processing, this will lead >> unnecessary wakeups from under layer net devices (E.g >> sock_def_readable() form tun). Rx will be slowed down in this >> way. This patch avoids this by stop polling socket during rx >> processing. A small drawback is that this introduces some overheads in >> light load case because of the extra start/stop polling, but single >> netperf TCP_RR does not notice any change. In a super heavy load case, >> e.g using pktgen to inject packet to guest, we get about ~8.8% >> improvement on pps: >> >> before: ~1240000 pkt/s >> after: ~1350000 pkt/s >> >> Signed-off-by: Jason Wang <jasowang@...hat.com> >> --- >> drivers/vhost/net.c | 56 +++++++++++++++++++++++++++-------------------------- >> 1 file changed, 29 insertions(+), 27 deletions(-) >> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c >> index 10ff494..e91603b 100644 >> --- a/drivers/vhost/net.c >> +++ b/drivers/vhost/net.c >> @@ -301,6 +301,32 @@ static bool vhost_can_busy_poll(struct vhost_dev *dev, >> !vhost_has_work(dev); >> } >> >> +static void vhost_net_disable_vq(struct vhost_net *n, >> + struct vhost_virtqueue *vq) >> +{ >> + struct vhost_net_virtqueue *nvq = >> + container_of(vq, struct vhost_net_virtqueue, vq); >> + struct vhost_poll *poll = n->poll + (nvq - n->vqs); >> + if (!vq->private_data) >> + return; >> + vhost_poll_stop(poll); >> +} >> + >> +static int vhost_net_enable_vq(struct vhost_net *n, >> + struct vhost_virtqueue *vq) >> +{ >> + struct vhost_net_virtqueue *nvq = >> + container_of(vq, struct vhost_net_virtqueue, vq); >> + struct vhost_poll *poll = n->poll + (nvq - n->vqs); >> + struct socket *sock; >> + >> + sock = vq->private_data; >> + if (!sock) >> + return 0; >> + >> + return vhost_poll_start(poll, sock->file); >> +} >> + >> static int vhost_net_tx_get_vq_desc(struct vhost_net *net, >> struct vhost_virtqueue *vq, >> struct iovec iov[], unsigned int iov_size, > BTW we might want to rename these functions, name no longer > reflects function ... Do you mean adding something reflect busy polling in the name? Then the name may be too long or have suggestion on the name? > > >> @@ -627,6 +653,7 @@ static void handle_rx(struct vhost_net *net) >> if (!sock) >> goto out; >> vhost_disable_notify(&net->dev, vq); >> + vhost_net_disable_vq(net, vq); >> >> vhost_hlen = nvq->vhost_hlen; >> sock_hlen = nvq->sock_hlen; >> @@ -715,9 +742,10 @@ static void handle_rx(struct vhost_net *net) >> total_len += vhost_len; >> if (unlikely(total_len >= VHOST_NET_WEIGHT)) { >> vhost_poll_queue(&vq->poll); >> - break; >> + goto out; >> } >> } >> + vhost_net_enable_vq(net, vq); > OK so if sock is readable but RX VQ is empty, this will > immediately schedule another round of handle_rx and so ad > infinitum, > > Looks like a bug. Yes it is, will change the above headcount check to: /* OK, now we need to know about added descriptors. */ if (!headcount) { if (unlikely(vhost_enable_notify(&net->dev, vq))) { /* They have slipped one in as we were * doing that: check again. */ vhost_disable_notify(&net->dev, vq); continue; } /* Nothing new? Wait for eventfd to tell us * they refilled. */ goto out; } > > >> out: >> mutex_unlock(&vq->mutex); >> } >> @@ -796,32 +824,6 @@ static int vhost_net_open(struct inode *inode, struct file *f) >> return 0; >> } >> >> -static void vhost_net_disable_vq(struct vhost_net *n, >> - struct vhost_virtqueue *vq) >> -{ >> - struct vhost_net_virtqueue *nvq = >> - container_of(vq, struct vhost_net_virtqueue, vq); >> - struct vhost_poll *poll = n->poll + (nvq - n->vqs); >> - if (!vq->private_data) >> - return; >> - vhost_poll_stop(poll); >> -} >> - >> -static int vhost_net_enable_vq(struct vhost_net *n, >> - struct vhost_virtqueue *vq) >> -{ >> - struct vhost_net_virtqueue *nvq = >> - container_of(vq, struct vhost_net_virtqueue, vq); >> - struct vhost_poll *poll = n->poll + (nvq - n->vqs); >> - struct socket *sock; >> - >> - sock = vq->private_data; >> - if (!sock) >> - return 0; >> - >> - return vhost_poll_start(poll, sock->file); >> -} >> - >> static struct socket *vhost_net_stop_vq(struct vhost_net *n, >> struct vhost_virtqueue *vq) >> { >> -- >> 1.8.3.1 > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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