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Date: Wed, 16 Feb 2022 16:42:36 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>,
virtualization <virtualization@...ts.linux-foundation.org>,
netdev <netdev@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org
Subject: Re: [PATCH v5 17/22] virtio_net: support rx/tx queue reset
On Wed, 16 Feb 2022 03:35:01 -0500, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> On Wed, Feb 16, 2022 at 03:56:13PM +0800, Xuan Zhuo wrote:
> > On Wed, 16 Feb 2022 12:14:11 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > > On Mon, Feb 14, 2022 at 4:14 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > > >
> > > > This patch implements the reset function of the rx, tx queues.
> > > >
> > > > Based on this function, it is possible to modify the ring num of the
> > > > queue. And quickly recycle the buffer in the queue.
> > > >
> > > > In the process of the queue disable, in theory, as long as virtio
> > > > supports queue reset, there will be no exceptions.
> > > >
> > > > However, in the process of the queue enable, there may be exceptions due to
> > > > memory allocation. In this case, vq is not available, but we still have
> > > > to execute napi_enable(). Because napi_disable is similar to a lock,
> > > > napi_enable must be called after calling napi_disable.
> > > >
> > > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > > ---
> > > > drivers/net/virtio_net.c | 123 +++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 123 insertions(+)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 9a1445236e23..a4ffd7cdf623 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -251,6 +251,11 @@ struct padded_vnet_hdr {
> > > > char padding[4];
> > > > };
> > > >
> > > > +static void virtnet_sq_free_unused_bufs(struct virtnet_info *vi,
> > > > + struct send_queue *sq);
> > > > +static void virtnet_rq_free_unused_bufs(struct virtnet_info *vi,
> > > > + struct receive_queue *rq);
> > > > +
> > > > static bool is_xdp_frame(void *ptr)
> > > > {
> > > > return (unsigned long)ptr & VIRTIO_XDP_FLAG;
> > > > @@ -1369,6 +1374,9 @@ static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
> > > > {
> > > > napi_enable(napi);
> > > >
> > > > + if (vq->reset)
> > > > + return;
> > > > +
> > > > /* If all buffers were filled by other side before we napi_enabled, we
> > > > * won't get another interrupt, so process any outstanding packets now.
> > > > * Call local_bh_enable after to trigger softIRQ processing.
> > > > @@ -1413,6 +1421,10 @@ static void refill_work(struct work_struct *work)
> > > > struct receive_queue *rq = &vi->rq[i];
> > > >
> > > > napi_disable(&rq->napi);
> > > > + if (rq->vq->reset) {
> > > > + virtnet_napi_enable(rq->vq, &rq->napi);
> > > > + continue;
> > > > + }
> > > > still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
> > > > virtnet_napi_enable(rq->vq, &rq->napi);
> > > >
> > > > @@ -1523,6 +1535,9 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
> > > > if (!sq->napi.weight || is_xdp_raw_buffer_queue(vi, index))
> > > > return;
> > > >
> > > > + if (sq->vq->reset)
> > > > + return;
> > > > +
> > > > if (__netif_tx_trylock(txq)) {
> > > > do {
> > > > virtqueue_disable_cb(sq->vq);
> > > > @@ -1769,6 +1784,114 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> > > > return NETDEV_TX_OK;
> > > > }
> > > >
> > > > +static int virtnet_rx_vq_disable(struct virtnet_info *vi,
> > > > + struct receive_queue *rq)
> > > > +{
> > > > + int err;
> > > > +
> > > > + napi_disable(&rq->napi);
> > > > +
> > > > + err = virtio_reset_vq(rq->vq);
> > > > + if (err)
> > > > + goto err;
> > > > +
> > > > + virtnet_rq_free_unused_bufs(vi, rq);
> > > > +
> > > > + vring_release_virtqueue(rq->vq);
> > > > +
> > > > + return 0;
> > > > +
> > > > +err:
> > > > + virtnet_napi_enable(rq->vq, &rq->napi);
> > > > + return err;
> > > > +}
> > > > +
> > > > +static int virtnet_tx_vq_disable(struct virtnet_info *vi,
> > > > + struct send_queue *sq)
> > > > +{
> > > > + struct netdev_queue *txq;
> > > > + int err, qindex;
> > > > +
> > > > + qindex = sq - vi->sq;
> > > > +
> > > > + txq = netdev_get_tx_queue(vi->dev, qindex);
> > > > + __netif_tx_lock_bh(txq);
> > > > +
> > > > + netif_stop_subqueue(vi->dev, qindex);
> > > > + virtnet_napi_tx_disable(&sq->napi);
> > > > +
> > > > + err = virtio_reset_vq(sq->vq);
> > > > + if (err) {
> > > > + virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> > > > + netif_start_subqueue(vi->dev, qindex);
> > > > +
> > > > + __netif_tx_unlock_bh(txq);
> > > > + return err;
> > > > + }
> > > > + __netif_tx_unlock_bh(txq);
> > > > +
> > > > + virtnet_sq_free_unused_bufs(vi, sq);
> > > > +
> > > > + vring_release_virtqueue(sq->vq);
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static int virtnet_tx_vq_enable(struct virtnet_info *vi, struct send_queue *sq)
> > > > +{
> > > > + int err;
> > > > +
> > > > + err = virtio_enable_resetq(sq->vq);
> > > > + if (!err)
> > > > + netif_start_subqueue(vi->dev, sq - vi->sq);
> > > > +
> > > > + virtnet_napi_tx_enable(vi, sq->vq, &sq->napi);
> > > > +
> > > > + return err;
> > > > +}
> > > > +
> > > > +static int virtnet_rx_vq_enable(struct virtnet_info *vi,
> > > > + struct receive_queue *rq)
> > > > +{
> > > > + int err;
> > >
> > > So the API should be design in a consistent way.
> > >
> > > In rx_vq_disable() we do:
> > >
> > > reset()
> > > detach_unused_bufs()
> > > vring_release_virtqueue()
> > >
> > > here it's better to exactly the reverse
> > >
> > > vring_attach_virtqueue() // this is the helper I guess in patch 5,
> > > reverse of the vring_release_virtqueue()
> > > try_refill_recv() // reverse of the detach_unused_bufs()
> > > enable_reset() // reverse of the reset
> >
> > Such an api is ok
> >
> > 1. reset()
> > 2. detach_unused_bufs()
> > 3. vring_release_virtqueue()
> > ---------------
> > 4. vring_attach_virtqueue()
> > 5. try_refill_recv()
> > 6. enable_reset()
> >
> >
> > But if, we just want to recycle the buffer without modifying the ring num. As
> > you mentioned before, in the case where the ring num is not modified, we don't
> > have to reallocate, but can use the original vring.
> >
> > 1. reset()
> > 2. detach_unused_bufs()
> > ---------------
> > 3. vring_reset_virtqueue() // just reset, no reallocate
> > 4. try_refill_recv()
> > 5. enable_reset()
> >
> > Thanks.
>
> Further, can we queue the buffers instead of detach_unused_bufs
> and just requeue them instead of try_refill_recv?
I think this is a good note, for support set_ringparam, this will be more
friendly.
I think I can implement this after the support for AF_XDP is done.
Thanks.
>
> > >
> > > So did for the tx (no need for refill in that case).
> > >
> > > > +
> > > > + err = virtio_enable_resetq(rq->vq);
> > > > +
> > > > + virtnet_napi_enable(rq->vq, &rq->napi);
> > > > +
> > > > + return err;
> > > > +}
> > > > +
> > > > +static int virtnet_rx_vq_reset(struct virtnet_info *vi, int i)
> > > > +{
> > > > + int err;
> > > > +
> > > > + err = virtnet_rx_vq_disable(vi, vi->rq + i);
> > > > + if (err)
> > > > + return err;
> > > > +
> > > > + err = virtnet_rx_vq_enable(vi, vi->rq + i);
> > > > + if (err)
> > > > + netdev_err(vi->dev,
> > > > + "enable rx reset vq fail: rx queue index: %d err: %d\n", i, err);
> > > > + return err;
> > > > +}
> > > > +
> > > > +static int virtnet_tx_vq_reset(struct virtnet_info *vi, int i)
> > > > +{
> > > > + int err;
> > > > +
> > > > + err = virtnet_tx_vq_disable(vi, vi->sq + i);
> > > > + if (err)
> > > > + return err;
> > > > +
> > > > + err = virtnet_tx_vq_enable(vi, vi->sq + i);
> > > > + if (err)
> > > > + netdev_err(vi->dev,
> > > > + "enable tx reset vq fail: tx queue index: %d err: %d\n", i, err);
> > > > + return err;
> > > > +}
> > > > +
> > > > /*
> > > > * Send command via the control virtqueue and check status. Commands
> > > > * supported by the hypervisor, as indicated by feature bits, should
> > > > --
> > > > 2.31.0
> > > >
> > >
>
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