netdev - Re: [PATCH bpf-next v5 6/7] bpf: Add "live packet" mode for XDP in bpf_prog

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Date:   Thu, 06 Jan 2022 15:28:41 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 6/7] bpf: Add "live packet" mode for XDP in
 bpf_prog_run()

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> On Mon, Jan 03, 2022 at 04:08:11PM +0100, Toke Høiland-Jørgensen wrote:
>> +static void xdp_test_run_init_page(struct page *page, void *arg)
>> +{
>> +	struct xdp_page_head *head = phys_to_virt(page_to_phys(page));
>> +	struct xdp_buff *new_ctx, *orig_ctx;
>> +	u32 headroom = XDP_PACKET_HEADROOM;
>> +	struct xdp_test_data *xdp = arg;
>> +	size_t frm_len, meta_len;
>> +	struct xdp_frame *frm;
>> +	void *data;
>> +
>> +	orig_ctx = xdp->orig_ctx;
>> +	frm_len = orig_ctx->data_end - orig_ctx->data_meta;
>> +	meta_len = orig_ctx->data - orig_ctx->data_meta;
>> +	headroom -= meta_len;
>> +
>> +	new_ctx = &head->ctx;
>> +	frm = &head->frm;
>> +	data = &head->data;
>> +	memcpy(data + headroom, orig_ctx->data_meta, frm_len);
>> +
>> +	xdp_init_buff(new_ctx, TEST_XDP_FRAME_SIZE, &xdp->rxq);
>> +	xdp_prepare_buff(new_ctx, data, headroom, frm_len, true);
>> +	new_ctx->data_meta = new_ctx->data + meta_len;
>
> data vs data_meta is the other way around, no?
>
> Probably needs a selftest to make sure.

Yup, you're right; nice catch! Will fix and add a test for it.

>> +static int xdp_recv_frames(struct xdp_frame **frames, int nframes,
>> +			   struct net_device *dev)
>> +{
>> +	gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
>> +	void *skbs[TEST_XDP_BATCH];
>> +	int i, n;
>> +	LIST_HEAD(list);
>> +
>> +	n = kmem_cache_alloc_bulk(skbuff_head_cache, gfp, nframes, skbs);
>> +	if (unlikely(n == 0)) {
>> +		for (i = 0; i < nframes; i++)
>> +			xdp_return_frame(frames[i]);
>> +		return -ENOMEM;
>> +	}
>> +
>> +	for (i = 0; i < nframes; i++) {
>> +		struct xdp_frame *xdpf = frames[i];
>> +		struct sk_buff *skb = skbs[i];
>> +
>> +		skb = __xdp_build_skb_from_frame(xdpf, skb, dev);
>> +		if (!skb) {
>> +			xdp_return_frame(xdpf);
>> +			continue;
>> +		}
>> +
>> +		list_add_tail(&skb->list, &list);
>> +	}
>> +	netif_receive_skb_list(&list);
>
> Does it need local_bh_disable() like cpumap does?

Yes, I think it probably does, actually. Or at least having it can
potentially improve performance since we're then sure that the whole
batch will be processed at once. Will add!

> I've applied patches 1 - 5.

Thanks! Will respin this and the selftest :)