From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933966AbcATOf3 (ORCPT ); Wed, 20 Jan 2016 09:35:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45393 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932261AbcATOf1 (ORCPT ); Wed, 20 Jan 2016 09:35:27 -0500 Date: Wed, 20 Jan 2016 16:35:24 +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 V2 3/3] vhost_net: basic polling support Message-ID: <20160120143524.GA27168@redhat.com> References: <1448951985-12385-1-git-send-email-jasowang@redhat.com> <1448951985-12385-4-git-send-email-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1448951985-12385-4-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 01, 2015 at 02:39:45PM +0800, Jason Wang wrote: > This patch tries to poll for new added tx buffer or socket receive > queue for a while at the end of tx/rx processing. The maximum time > spent on polling were specified through a new kind of vring ioctl. > > Signed-off-by: Jason Wang > --- > drivers/vhost/net.c | 72 ++++++++++++++++++++++++++++++++++++++++++---- > drivers/vhost/vhost.c | 15 ++++++++++ > drivers/vhost/vhost.h | 1 + > include/uapi/linux/vhost.h | 11 +++++++ > 4 files changed, 94 insertions(+), 5 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 9eda69e..ce6da77 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -287,6 +287,41 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) > rcu_read_unlock_bh(); > } > > +static inline unsigned long busy_clock(void) > +{ > + return local_clock() >> 10; > +} > + > +static bool vhost_can_busy_poll(struct vhost_dev *dev, > + unsigned long endtime) > +{ > + return likely(!need_resched()) && > + likely(!time_after(busy_clock(), endtime)) && > + likely(!signal_pending(current)) && > + !vhost_has_work(dev) && > + single_task_running(); > +} > + > +static int vhost_net_tx_get_vq_desc(struct vhost_net *net, > + struct vhost_virtqueue *vq, > + struct iovec iov[], unsigned int iov_size, > + unsigned int *out_num, unsigned int *in_num) > +{ > + unsigned long uninitialized_var(endtime); > + > + if (vq->busyloop_timeout) { > + preempt_disable(); > + endtime = busy_clock() + vq->busyloop_timeout; > + while (vhost_can_busy_poll(vq->dev, endtime) && > + !vhost_vq_more_avail(vq->dev, vq)) > + cpu_relax(); > + preempt_enable(); > + } Isn't there a way to call all this after vhost_get_vq_desc? First, this will reduce the good path overhead as you won't have to play with timers and preemption. Second, this will reduce the chance of a pagefault on avail ring read. > + > + return vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), > + out_num, in_num, NULL, NULL); > +} > + > /* Expects to be always run from workqueue - which acts as > * read-size critical section for our kind of RCU. */ > static void handle_tx(struct vhost_net *net) > @@ -331,10 +366,9 @@ static void handle_tx(struct vhost_net *net) > % UIO_MAXIOV == nvq->done_idx)) > break; > > - head = vhost_get_vq_desc(vq, vq->iov, > - ARRAY_SIZE(vq->iov), > - &out, &in, > - NULL, NULL); > + head = vhost_net_tx_get_vq_desc(net, vq, vq->iov, > + ARRAY_SIZE(vq->iov), > + &out, &in); > /* On error, stop handling until the next kick. */ > if (unlikely(head < 0)) > break; > @@ -435,6 +469,34 @@ static int peek_head_len(struct sock *sk) > return len; > } > > +static int vhost_net_peek_head_len(struct vhost_net *net, struct sock *sk) Need a hint that it's rx related in the name. > +{ > + struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX]; > + struct vhost_virtqueue *vq = &nvq->vq; > + unsigned long uninitialized_var(endtime); > + > + if (vq->busyloop_timeout) { > + mutex_lock(&vq->mutex); This appears to be called under vq mutex in handle_rx. So how does this work then? > + vhost_disable_notify(&net->dev, vq); This appears to be called after disable notify in handle_rx - so why disable here again? > + > + preempt_disable(); > + endtime = busy_clock() + vq->busyloop_timeout; > + > + while (vhost_can_busy_poll(&net->dev, endtime) && > + skb_queue_empty(&sk->sk_receive_queue) && > + !vhost_vq_more_avail(&net->dev, vq)) > + cpu_relax(); This seems to mix in several items. RX queue is normally not empty. I don't think we need to poll for that. So IMHO we only need to poll for sk_receive_queue really. > + > + preempt_enable(); > + > + if (vhost_enable_notify(&net->dev, vq)) > + vhost_poll_queue(&vq->poll); But vhost_enable_notify returns true on queue not empty. So in fact this will requeue on good path - does not make sense to me. > + mutex_unlock(&vq->mutex); > + } > + Same comment as for get vq desc here: don't slow down the good path. > + return peek_head_len(sk); > +} > + > /* This is a multi-buffer version of vhost_get_desc, that works if > * vq has read descriptors only. > * @vq - the relevant virtqueue > @@ -553,7 +615,7 @@ static void handle_rx(struct vhost_net *net) > vq->log : NULL; > mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF); > > - while ((sock_len = peek_head_len(sock->sk))) { > + while ((sock_len = vhost_net_peek_head_len(net, sock->sk))) { > sock_len += sock_hlen; > vhost_len = sock_len + vhost_hlen; > headcount = get_rx_bufs(vq, vq->heads, vhost_len, > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 4f45a03..b8ca873 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -285,6 +285,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > vq->memory = NULL; > vq->is_le = virtio_legacy_is_little_endian(); > vhost_vq_reset_user_be(vq); > + vq->busyloop_timeout = 0; > } > > static int vhost_worker(void *data) > @@ -747,6 +748,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > struct vhost_vring_state s; > struct vhost_vring_file f; > struct vhost_vring_addr a; > + struct vhost_vring_busyloop_timeout t; > u32 idx; > long r; > > @@ -919,6 +921,19 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > case VHOST_GET_VRING_ENDIAN: > r = vhost_get_vring_endian(vq, idx, argp); > break; > + case VHOST_SET_VRING_BUSYLOOP_TIMEOUT: > + if (copy_from_user(&t, argp, sizeof(t))) { > + r = -EFAULT; > + break; > + } > + vq->busyloop_timeout = t.timeout; > + break; > + case VHOST_GET_VRING_BUSYLOOP_TIMEOUT: > + t.index = idx; > + t.timeout = vq->busyloop_timeout; > + if (copy_to_user(argp, &t, sizeof(t))) > + r = -EFAULT; > + break; > default: > r = -ENOIOCTLCMD; > } > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index 2f3c57c..4b7d4fa 100644 > --- a/drivers/vhost/vhost.h > +++ b/drivers/vhost/vhost.h > @@ -115,6 +115,7 @@ struct vhost_virtqueue { > /* Ring endianness requested by userspace for cross-endian support. */ > bool user_be; > #endif > + u32 busyloop_timeout; > }; > > struct vhost_dev { > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > index ab373191..eaf6c33 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -27,6 +27,11 @@ struct vhost_vring_file { > > }; > > +struct vhost_vring_busyloop_timeout { > + unsigned int index; > + unsigned int timeout; > +}; > + So why not reuse vhost_vring_state then? > struct vhost_vring_addr { > unsigned int index; > /* Option flags. */ > @@ -126,6 +131,12 @@ struct vhost_memory { > #define VHOST_SET_VRING_CALL _IOW(VHOST_VIRTIO, 0x21, struct vhost_vring_file) > /* Set eventfd to signal an error */ > #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file) > +/* Set busy loop timeout */ Units? > +#define VHOST_SET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x23, \ > + struct vhost_vring_busyloop_timeout) > +/* Get busy loop timeout */ > +#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24, \ > + struct vhost_vring_busyloop_timeout) > > /* VHOST_NET specific defines */ > > -- > 2.5.0