From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753293Ab3CKI3I (ORCPT ); Mon, 11 Mar 2013 04:29:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5264 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205Ab3CKI3D (ORCPT ); Mon, 11 Mar 2013 04:29:03 -0400 Date: Mon, 11 Mar 2013 10:29:23 +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: <20130311082923.GB21086@redhat.com> References: <1362630716-57674-1-git-send-email-jasowang@redhat.com> <20130310165030.GA13687@redhat.com> <513D8316.90907@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <513D8316.90907@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 11, 2013 at 03:09:10PM +0800, Jason Wang wrote: > On 03/11/2013 12:50 AM, Michael S. Tsirkin wrote: > > 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. > > I think then it may damage the performance at least for tx. We > conditionally enable the tx polling in the past to reduce the > unnecessary wakeups of vhost thead when zerocopy or sndbuf is used. If > we don't stop the polling, after each packet were transmitted, > tap/macvtap will try to wakeup the vhost thread. It won't actually. static void macvtap_sock_write_space(struct sock *sk) { wait_queue_head_t *wqueue; if (!sock_writeable(sk) || !test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags)) return; wqueue = sk_sleep(sk); if (wqueue && waitqueue_active(wqueue)) wake_up_interruptible_poll(wqueue, POLLOUT | POLLWRNORM | POLLWRBAND); } As long as SOCK_ASYNC_NOSPACE is not set, there's no wakeup. > Actually, I'm considering the reverse direction. Looks like we can > disable the rx polling like what we do for tx in handle_tx() to reduce > the uncessary wakeups. > > 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 > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html