From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753149Ab3CKI0G (ORCPT ); Mon, 11 Mar 2013 04:26:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64349 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205Ab3CKI0E (ORCPT ); Mon, 11 Mar 2013 04:26:04 -0400 Date: Mon, 11 Mar 2013 10:26:24 +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: <20130311082533.GA21086@redhat.com> References: <1362630716-57674-1-git-send-email-jasowang@redhat.com> <20130310165030.GA13687@redhat.com> <513D8316.90907@redhat.com> <513D88BC.4010108@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <513D88BC.4010108@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 03:33:16PM +0800, Jason Wang wrote: > On 03/11/2013 03:09 PM, 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. > > Or for zerocopy, looks like we can in fact just depends on > ubuf->callback in stead of tx polling to wakeup tx thread to do tx > completion, so we can even drop the num_pends and VHOST_MAX_PEND stuffs. I think we still need to limit the number of outstanding buffers so VHOST_MAX_PEND needs to stay. I'm not against switching to callback for this but let's make this a separate change. > > 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 > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/