From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752857Ab3CJQuS (ORCPT ); Sun, 10 Mar 2013 12:50:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9816 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750956Ab3CJQuQ (ORCPT ); Sun, 10 Mar 2013 12:50:16 -0400 Date: Sun, 10 Mar 2013 18:50:30 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vhost_net: remove tx polling state Message-ID: <20130310165030.GA13687@redhat.com> References: <1362630716-57674-1-git-send-email-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1362630716-57674-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 07, 2013 at 12:31:56PM +0800, Jason Wang wrote: > After commit 2b8b328b61c799957a456a5a8dab8cc7dea68575 (vhost_net: handle polling > errors when setting backend), we in fact track the polling state through > poll->wqh, so there's no need to duplicate the work with an extra > vhost_net_polling_state. So this patch removes this and make the code simpler. > > Signed-off-by: Jason Wang I'd prefer a more radical approach, since I think it can be even simpler: tap and macvtap backends both only send events when tx queue overruns which should almost never happen. So let's just start polling when VQ is enabled drop all poll_start/stop calls on data path. The optimization was written for packet socket backend but I know of no one caring about performance of that one that much. Needs a bit of perf testing to make sure I didn't miss anything though but it's not 3.9 material anyway so there's no rush. > --- > drivers/vhost/net.c | 60 ++++++++---------------------------------------- > drivers/vhost/vhost.c | 3 ++ > 2 files changed, 13 insertions(+), 50 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 959b1cd..d1a03dd 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -64,20 +64,10 @@ enum { > VHOST_NET_VQ_MAX = 2, > }; > > -enum vhost_net_poll_state { > - VHOST_NET_POLL_DISABLED = 0, > - VHOST_NET_POLL_STARTED = 1, > - VHOST_NET_POLL_STOPPED = 2, > -}; > - > struct vhost_net { > struct vhost_dev dev; > struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX]; > struct vhost_poll poll[VHOST_NET_VQ_MAX]; > - /* Tells us whether we are polling a socket for TX. > - * We only do this when socket buffer fills up. > - * Protected by tx vq lock. */ > - enum vhost_net_poll_state tx_poll_state; > /* Number of TX recently submitted. > * Protected by tx vq lock. */ > unsigned tx_packets; > @@ -155,28 +145,6 @@ static void copy_iovec_hdr(const struct iovec *from, struct iovec *to, > } > } > > -/* Caller must have TX VQ lock */ > -static void tx_poll_stop(struct vhost_net *net) > -{ > - if (likely(net->tx_poll_state != VHOST_NET_POLL_STARTED)) > - return; > - vhost_poll_stop(net->poll + VHOST_NET_VQ_TX); > - net->tx_poll_state = VHOST_NET_POLL_STOPPED; > -} > - > -/* Caller must have TX VQ lock */ > -static int tx_poll_start(struct vhost_net *net, struct socket *sock) > -{ > - int ret; > - > - if (unlikely(net->tx_poll_state != VHOST_NET_POLL_STOPPED)) > - return 0; > - ret = vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file); > - if (!ret) > - net->tx_poll_state = VHOST_NET_POLL_STARTED; > - return ret; > -} > - > /* In case of DMA done not in order in lower device driver for some reason. > * upend_idx is used to track end of used idx, done_idx is used to track head > * of used idx. Once lower device DMA done contiguously, we will signal KVM > @@ -231,6 +199,7 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) > static void handle_tx(struct vhost_net *net) > { > struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX]; > + struct vhost_poll *poll = net->poll + VHOST_NET_VQ_TX; > unsigned out, in, s; > int head; > struct msghdr msg = { > @@ -256,7 +225,7 @@ static void handle_tx(struct vhost_net *net) > wmem = atomic_read(&sock->sk->sk_wmem_alloc); > if (wmem >= sock->sk->sk_sndbuf) { > mutex_lock(&vq->mutex); > - tx_poll_start(net, sock); > + vhost_poll_start(poll, sock->file); > mutex_unlock(&vq->mutex); > return; > } > @@ -265,7 +234,7 @@ static void handle_tx(struct vhost_net *net) > vhost_disable_notify(&net->dev, vq); > > if (wmem < sock->sk->sk_sndbuf / 2) > - tx_poll_stop(net); > + vhost_poll_stop(poll); > hdr_size = vq->vhost_hlen; > zcopy = vq->ubufs; > > @@ -287,7 +256,7 @@ static void handle_tx(struct vhost_net *net) > > wmem = atomic_read(&sock->sk->sk_wmem_alloc); > if (wmem >= sock->sk->sk_sndbuf * 3 / 4) { > - tx_poll_start(net, sock); > + vhost_poll_start(poll, sock->file); > set_bit(SOCK_ASYNC_NOSPACE, &sock->flags); > break; > } > @@ -298,7 +267,7 @@ static void handle_tx(struct vhost_net *net) > (vq->upend_idx - vq->done_idx) : > (vq->upend_idx + UIO_MAXIOV - vq->done_idx); > if (unlikely(num_pends > VHOST_MAX_PEND)) { > - tx_poll_start(net, sock); > + vhost_poll_start(poll, sock->file); > set_bit(SOCK_ASYNC_NOSPACE, &sock->flags); > break; > } > @@ -364,7 +333,7 @@ static void handle_tx(struct vhost_net *net) > } > vhost_discard_vq_desc(vq, 1); > if (err == -EAGAIN || err == -ENOBUFS) > - tx_poll_start(net, sock); > + vhost_poll_start(poll, sock->file); > break; > } > if (err != len) > @@ -627,7 +596,6 @@ static int vhost_net_open(struct inode *inode, struct file *f) > > vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev); > vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev); > - n->tx_poll_state = VHOST_NET_POLL_DISABLED; > > f->private_data = n; > > @@ -637,32 +605,24 @@ static int vhost_net_open(struct inode *inode, struct file *f) > static void vhost_net_disable_vq(struct vhost_net *n, > struct vhost_virtqueue *vq) > { > + struct vhost_poll *poll = n->poll + (vq - n->vqs); > if (!vq->private_data) > return; > - if (vq == n->vqs + VHOST_NET_VQ_TX) { > - tx_poll_stop(n); > - n->tx_poll_state = VHOST_NET_POLL_DISABLED; > - } else > - vhost_poll_stop(n->poll + VHOST_NET_VQ_RX); > + vhost_poll_stop(poll); > } > > static int vhost_net_enable_vq(struct vhost_net *n, > struct vhost_virtqueue *vq) > { > + struct vhost_poll *poll = n->poll + (vq - n->vqs); > struct socket *sock; > - int ret; > > sock = rcu_dereference_protected(vq->private_data, > lockdep_is_held(&vq->mutex)); > if (!sock) > return 0; > - if (vq == n->vqs + VHOST_NET_VQ_TX) { > - n->tx_poll_state = VHOST_NET_POLL_STOPPED; > - ret = tx_poll_start(n, sock); > - } else > - ret = vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file); > > - return ret; > + return vhost_poll_start(poll, sock->file); > } > > static struct socket *vhost_net_stop_vq(struct vhost_net *n, > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 9759249..4eecdb8 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -89,6 +89,9 @@ int vhost_poll_start(struct vhost_poll *poll, struct file *file) > unsigned long mask; > int ret = 0; > > + if (poll->wqh) > + return 0; > + > mask = file->f_op->poll(file, &poll->table); > if (mask) > vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask); > -- > 1.7.1