Re: [PATCH v7 net-next] virtio-net: support XDP when not more queues

[Jason Wang <jasowang@xxxxxxxxxx>]

On 2021/3/9 10:31 上午, Xuan Zhuo wrote:
> On Tue, 9 Mar 2021 10:17:16 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > On 2021/3/8 4:52 下午, Xuan Zhuo wrote:
> > > The number of queues implemented by many virtio backends is limited,
> > > especially some machines have a large number of CPUs. In this case, it
> > > is often impossible to allocate a separate queue for
> > > XDP_TX/XDP_REDIRECT, then xdp cannot be loaded to work, even xdp does
> > > not use the XDP_TX/XDP_REDIRECT.
> > >
> > > This patch allows XDP_TX/XDP_REDIRECT to run by reuse the existing SQ
> > > with __netif_tx_lock() hold when there are not enough queues.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
> > > ---
> > > v7: 1. use macros to implement get/put
> > >       2. remove 'flag'. (suggested by Jason Wang)
> > >
> > > v6: 1. use __netif_tx_acquire()/__netif_tx_release(). (suggested by Jason Wang)
> > >       2. add note for why not lock. (suggested by Jason Wang)
> > >       3. Use variable 'flag' to record with or without locked.  It is not safe to
> > >          use curr_queue_pairs in "virtnet_put_xdp_sq", because it may changed after
> > >          "virtnet_get_xdp_sq".
> > >
> > > v5: change subject from 'support XDP_TX when not more queues'
> > >
> > > v4: make sparse happy
> > >       suggested by Jakub Kicinski
> > >
> > > v3: add warning when no more queues
> > >       suggested by Jesper Dangaard Brouer
> > >
> > >    drivers/net/virtio_net.c | 55 ++++++++++++++++++++++++++++++++++++------------
> > >    1 file changed, 42 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index ba8e637..5ce40ec 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -195,6 +195,9 @@ struct virtnet_info {
> > >    	/* # of XDP queue pairs currently used by the driver */
> > >    	u16 xdp_queue_pairs;
> > >
> > > +	/* xdp_queue_pairs may be 0, when xdp is already loaded. So add this. */
> > > +	bool xdp_enabled;
> > > +
> > >    	/* I like... big packets and I cannot lie! */
> > >    	bool big_packets;
> > >
> > > @@ -481,12 +484,34 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
> > >    	return 0;
> > >    }
> > >
> > > -static struct send_queue *virtnet_xdp_sq(struct virtnet_info *vi)
> > > -{
> > > -	unsigned int qp;
> > > -
> > > -	qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
> > > -	return &vi->sq[qp];
> > > +/* when vi->curr_queue_pairs > nr_cpu_ids, the txq/sq is only used for xdp tx on
> > > + * the current cpu, so it does not need to be locked.
> > > + */
> > > +#define virtnet_xdp_get_sq(vi) ({                                         \
> > > +	struct netdev_queue *txq;                                         \
> > > +	typeof(vi) v = (vi);                                              \
> >
> > Any reason for not using vi directly?
> >
> > Other looks good.
> >
> > Thanks
> Using vi directly, I got an error by checkpatch.pl:
>
> 	Macro argument reuse 'vi' - possible side-effects
>
> more info: https://gcc.gnu.org/onlinedocs/cpp/Duplication-of-Side-Effects.html
>
> Thanks.


Ok.

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks


> > > +	unsigned int qp;                                                  \
> > > +	if (v->curr_queue_pairs > nr_cpu_ids) {                           \
> > > +		qp = v->curr_queue_pairs - v->xdp_queue_pairs;            \
> > > +		qp += smp_processor_id();                                 \
> > > +		txq = netdev_get_tx_queue(v->dev, qp);                    \
> > > +		__netif_tx_acquire(txq);                                  \
> > > +	} else {                                                          \
> > > +		qp = smp_processor_id() % v->curr_queue_pairs;            \
> > > +		txq = netdev_get_tx_queue(v->dev, qp);                    \
> > > +		__netif_tx_lock(txq, raw_smp_processor_id());             \
> > > +	}                                                                 \
> > > +	v->sq + qp;                                                       \
> > > +})
> > > +
> > > +#define virtnet_xdp_put_sq(vi, q) {                                       \
> > > +	struct netdev_queue *txq;                                         \
> > > +	typeof(vi) v = (vi);                                              \
> > > +	txq = netdev_get_tx_queue(v->dev, (q) - v->sq);                   \
> > > +	if (v->curr_queue_pairs > nr_cpu_ids)                             \
> > > +		__netif_tx_release(txq);                                  \
> > > +	else                                                              \
> > > +		__netif_tx_unlock(txq);                                   \
> > >    }
> > >
> > >    static int virtnet_xdp_xmit(struct net_device *dev,
> > > @@ -512,7 +537,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> > >    	if (!xdp_prog)
> > >    		return -ENXIO;
> > >
> > > -	sq = virtnet_xdp_sq(vi);
> > > +	sq = virtnet_xdp_get_sq(vi);
> > >
> > >    	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
> > >    		ret = -EINVAL;
> > > @@ -560,12 +585,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> > >    	sq->stats.kicks += kicks;
> > >    	u64_stats_update_end(&sq->stats.syncp);
> > >
> > > +	virtnet_xdp_put_sq(vi, sq);
> > >    	return ret;
> > >    }
> > >
> > >    static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
> > >    {
> > > -	return vi->xdp_queue_pairs ? VIRTIO_XDP_HEADROOM : 0;
> > > +	return vi->xdp_enabled ? VIRTIO_XDP_HEADROOM : 0;
> > >    }
> > >
> > >    /* We copy the packet for XDP in the following cases:
> > > @@ -1457,12 +1483,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
> > >    		xdp_do_flush();
> > >
> > >    	if (xdp_xmit & VIRTIO_XDP_TX) {
> > > -		sq = virtnet_xdp_sq(vi);
> > > +		sq = virtnet_xdp_get_sq(vi);
> > >    		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
> > >    			u64_stats_update_begin(&sq->stats.syncp);
> > >    			sq->stats.kicks++;
> > >    			u64_stats_update_end(&sq->stats.syncp);
> > >    		}
> > > +		virtnet_xdp_put_sq(vi, sq);
> > >    	}
> > >
> > >    	return received;
> > > @@ -2417,10 +2444,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> > >
> > >    	/* XDP requires extra queues for XDP_TX */
> > >    	if (curr_qp + xdp_qp > vi->max_queue_pairs) {
> > > -		NL_SET_ERR_MSG_MOD(extack, "Too few free TX rings available");
> > > -		netdev_warn(dev, "request %i queues but max is %i\n",
> > > +		netdev_warn(dev, "XDP request %i queues but max is %i. XDP_TX and XDP_REDIRECT will operate in a slower locked tx mode.\n",
> > >    			    curr_qp + xdp_qp, vi->max_queue_pairs);
> > > -		return -ENOMEM;
> > > +		xdp_qp = 0;
> > >    	}
> > >
> > >    	old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
> > > @@ -2454,11 +2480,14 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> > >    	vi->xdp_queue_pairs = xdp_qp;
> > >
> > >    	if (prog) {
> > > +		vi->xdp_enabled = true;
> > >    		for (i = 0; i < vi->max_queue_pairs; i++) {
> > >    			rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
> > >    			if (i == 0 && !old_prog)
> > >    				virtnet_clear_guest_offloads(vi);
> > >    		}
> > > +	} else {
> > > +		vi->xdp_enabled = false;
> > >    	}
> > >
> > >    	for (i = 0; i < vi->max_queue_pairs; i++) {
> > > @@ -2526,7 +2555,7 @@ static int virtnet_set_features(struct net_device *dev,
> > >    	int err;
> > >
> > >    	if ((dev->features ^ features) & NETIF_F_LRO) {
> > > -		if (vi->xdp_queue_pairs)
> > > +		if (vi->xdp_enabled)
> > >    			return -EBUSY;
> > >
> > >    		if (features & NETIF_F_LRO)
> > > --
> > > 1.8.3.1