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Date: Wed, 16 Feb 2022 15:56:13 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization <virtualization@...ts.linux-foundation.org>,
netdev <netdev@...r.kernel.org>,
"Michael S. Tsirkin" <mst@...hat.com>,
"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 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.
>
> 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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