netdev - Re: [RFC PATCH v7] vmxnet3: Add XDP support.

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Date:   Thu, 22 Dec 2022 22:25:51 +0100
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     William Tu <u9012063@...il.com>, netdev@...r.kernel.org
Cc:     tuc@...are.com, gyang@...are.com, doshir@...are.com
Subject: Re: [RFC PATCH v7] vmxnet3: Add XDP support.

On 22.12.22 16:46, William Tu wrote:
> @@ -1776,6 +1800,7 @@ vmxnet3_rq_cleanup(struct vmxnet3_rx_queue *rq,
>   
>   	rq->comp_ring.gen = VMXNET3_INIT_GEN;
>   	rq->comp_ring.next2proc = 0;
> +	rq->xdp_bpf_prog = NULL;

Reference to BPF program is lost without calling bpf_prog_put(). Are you
sure this is ok? This function is called during ndo_stop too.

[...]

> +static int
> +vmxnet3_xdp_set(struct net_device *netdev, struct netdev_bpf *bpf,
> +		struct netlink_ext_ack *extack)
> +{
> +	struct vmxnet3_adapter *adapter = netdev_priv(netdev);
> +	struct bpf_prog *new_bpf_prog = bpf->prog;
> +	struct bpf_prog *old_bpf_prog;
> +	bool need_update;
> +	bool running;
> +	int err = 0;
> +
> +	if (new_bpf_prog && netdev->mtu > VMXNET3_XDP_MAX_MTU) {
> +		NL_SET_ERR_MSG_MOD(extack, "MTU too large for XDP");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	old_bpf_prog = READ_ONCE(adapter->rx_queue[0].xdp_bpf_prog);

Wouldn't it be simpler if xdp_bpf_prog is move from rx_queue to
adapter?

[...]

> +/* This is the main xdp call used by kernel to set/unset eBPF program. */
> +int
> +vmxnet3_xdp(struct net_device *netdev, struct netdev_bpf *bpf)
> +{
> +	switch (bpf->command) {
> +	case XDP_SETUP_PROG:
> +		netdev_dbg(netdev, "XDP: set program to ");

Did you forget to delete this debug output?

[...]

> +int
> +vmxnet3_xdp_xmit(struct net_device *dev,
> +		 int n, struct xdp_frame **frames, u32 flags)
> +{
> +	struct vmxnet3_adapter *adapter;
> +	struct vmxnet3_tx_queue *tq;
> +	struct netdev_queue *nq;
> +	int i, err, cpu;
> +	int nxmit = 0;
> +	int tq_number;
> +
> +	adapter = netdev_priv(dev);
> +
> +	if (unlikely(test_bit(VMXNET3_STATE_BIT_QUIESCED, &adapter->state)))
> +		return -ENETDOWN;
> +	if (unlikely(test_bit(VMXNET3_STATE_BIT_RESETTING, &adapter->state)))
> +		return -EINVAL;
> +
> +	tq_number = adapter->num_tx_queues;
> +	cpu = smp_processor_id();
> +	tq = &adapter->tx_queue[cpu % tq_number];
> +	if (tq->stopped)
> +		return -ENETDOWN;
> +
> +	nq = netdev_get_tx_queue(adapter->netdev, tq->qid);
> +
> +	__netif_tx_lock(nq, cpu);
> +	for (i = 0; i < n; i++) {
> +		err = vmxnet3_xdp_xmit_frame(adapter, frames[i], tq);
> +		/* vmxnet3_xdp_xmit_frame has copied the data
> +		 * to skb, so we free xdp frame below.
> +		 */
> +		get_page(virt_to_page(frames[i]->data));
> +		xdp_return_frame(frames[i]);
> +		if (err) {
> +			tq->stats.xdp_xmit_err++;
> +			break;
> +		}
> +		nxmit++;

You could just use the loop iterator and drop nxmit. I got this comment
for one of my XDP patches from Saeed Mahameed.

[...]

Did you consider to split this patch into multiple patches to make
review easier?

Gerhard