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 <jasowang@xxxxxxxxxx> >> 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. > 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@xxxxxxxxxxxxxxx >> 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@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html