netdev - Re: [PATCH RFC net-next v19] vmxnet3: Add XDP support.

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Date:   Fri, 31 Mar 2023 17:43:09 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     William Tu <u9012063@...il.com>
CC:     <netdev@...r.kernel.org>, <jsankararama@...are.com>,
        <gyang@...are.com>, <doshir@...are.com>,
        <alexander.duyck@...il.com>, <alexandr.lobakin@...el.com>,
        <bang@...are.com>, <maciej.fijalkowski@...el.com>,
        <witu@...dia.com>, <horatiu.vultur@...rochip.com>,
        <error27@...il.com>, Alexander Duyck <alexanderduyck@...com>
Subject: Re: [PATCH RFC net-next v19] vmxnet3: Add XDP support.

From: William Tu <u9012063@...il.com>
Date: Sat, 25 Mar 2023 10:28:28 -0700

Sorry for the late reply, I've been busy :s

> From: William Tu <u9012063@...il.com>
> 
> The patch adds native-mode XDP support: XDP DROP, PASS, TX, and REDIRECT.
> 
> Background:

[...]

> +static int
> +vmxnet3_run_xdp(struct vmxnet3_rx_queue *rq, struct xdp_buff *xdp,
> +		struct bpf_prog *prog)
> +{
> +	struct xdp_frame *xdpf;
> +	struct page *page;
> +	int err;
> +	u32 act;
> +
> +	act = bpf_prog_run_xdp(prog, xdp);
> +	rq->stats.xdp_packets++;

I think you can increment it *before* running the program, so that
there'll be as tiny time gap as possible.

> +	page = virt_to_page(xdp->data_hard_start);

You don't need it for PASS and REDIRECT.

> +
> +	switch (act) {
> +	case XDP_PASS:
> +		return act;
> +	case XDP_REDIRECT:
> +		err = xdp_do_redirect(rq->adapter->netdev, xdp, prog);
> +		if (!err)
> +			rq->stats.xdp_redirects++;
> +		else
> +			rq->stats.xdp_drops++;

BTW, if you get @err here, shouldn't you recycle the page, just like in
TX case?

> +		return act;
> +	case XDP_TX:
> +		xdpf = xdp_convert_buff_to_frame(xdp);
> +		if (unlikely(!xdpf ||
> +			     vmxnet3_xdp_xmit_back(rq->adapter, xdpf))) {
> +			rq->stats.xdp_drops++;
> +			page_pool_recycle_direct(rq->page_pool, page);
> +		} else {
> +			rq->stats.xdp_tx++;
> +		}
> +		return act;
> +	default:
> +		bpf_warn_invalid_xdp_action(rq->adapter->netdev, prog, act);
> +		fallthrough;
> +	case XDP_ABORTED:
> +		trace_xdp_exception(rq->adapter->netdev, prog, act);
> +		rq->stats.xdp_aborted++;
> +		break;
> +	case XDP_DROP:
> +		rq->stats.xdp_drops++;
> +		break;
> +	}
> +
> +	page_pool_recycle_direct(rq->page_pool, page);
> +
> +	return act;
> +}

[...]

> +	xdp_init_buff(&xdp, PAGE_SIZE, &rq->xdp_rxq);
> +	xdp_prepare_buff(&xdp, page_address(page), rq->page_pool->p.offset,
> +			 len, false);
> +	xdp_buff_clear_frags_flag(&xdp);
> +
> +	/* Must copy the data because it's at dataring. */
> +	memcpy(xdp.data, data, len);
> +
> +	rcu_read_lock();

Where's the corresponding unlock?

> +	xdp_prog = rcu_dereference(rq->adapter->xdp_bpf_prog);
> +	if (!xdp_prog) {
> +		act = XDP_PASS;
> +		goto out_skb;
> +	}
> +	act = vmxnet3_run_xdp(rq, &xdp, xdp_prog);
> +
> +	if (act == XDP_PASS) {
> +out_skb:
> +		*skb_xdp_pass = vmxnet3_build_skb(rq, page, &xdp);
> +		if (!*skb_xdp_pass)
> +			return XDP_DROP;
> +	}
> +
> +	/* No need to refill. */
> +	return act;

Maybe

	act = vmxnet3_run_xdp(rq, &xdp, xdp_prog);
	if (act != XDP_PASS)
		return act;

out_skb:
	*skb_xdp_pass = vmxnet3_build_skb(rq, page, &xdp);

	return likely(*skb_xdp_pass) ? act : XDP_DROP;

?

> +}
> +
> +int
> +vmxnet3_process_xdp(struct vmxnet3_adapter *adapter,
> +		    struct vmxnet3_rx_queue *rq,
> +		    struct Vmxnet3_RxCompDesc *rcd,
> +		    struct vmxnet3_rx_buf_info *rbi,
> +		    struct Vmxnet3_RxDesc *rxd,
> +		    struct sk_buff **skb_xdp_pass)
[...]

Thanks,
Olek