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Message-ID: <20200123032154-mutt-send-email-mst@kernel.org>
Date: Thu, 23 Jan 2020 03:23:22 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org, prashantbhole.linux@...il.com,
jasowang@...hat.com, davem@...emloft.net,
jakub.kicinski@...ronome.com, jbrouer@...hat.com, toke@...hat.com,
toshiaki.makita1@...il.com, daniel@...earbox.net,
john.fastabend@...il.com, ast@...nel.org, kafai@...com,
songliubraving@...com, yhs@...com, andriin@...com,
dsahern@...il.com
Subject: Re: [PATCH bpf-next 10/12] tun: run XDP program in tx path
On Wed, Jan 22, 2020 at 06:42:08PM -0700, David Ahern wrote:
> From: Prashant Bhole <prashantbhole.linux@...il.com>
>
> Run the XDP program as soon as packet is removed from the ptr
> ring. Since this is XDP in tx path, the traditional handling of
> XDP actions XDP_TX/REDIRECT isn't valid. For this reason we call
> do_xdp_generic_core instead of do_xdp_generic. do_xdp_generic_core
> just runs the program and leaves the action handling to us.
>
> Signed-off-by: Prashant Bhole <prashantbhole.linux@...il.com>
> ---
> drivers/net/tun.c | 153 +++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 150 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index b6bac773f2a0..71bcd4ec2571 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -130,6 +130,7 @@ struct tap_filter {
> /* MAX_TAP_QUEUES 256 is chosen to allow rx/tx queues to be equal
> * to max number of VCPUs in guest. */
> #define MAX_TAP_QUEUES 256
> +#define MAX_TAP_BATCH 64
> #define MAX_TAP_FLOWS 4096
>
> #define TUN_FLOW_EXPIRE (3 * HZ)
> @@ -175,6 +176,7 @@ struct tun_file {
> struct tun_struct *detached;
> struct ptr_ring tx_ring;
> struct xdp_rxq_info xdp_rxq;
> + void *pkt_ptrs[MAX_TAP_BATCH];
> };
>
> struct tun_page {
> @@ -2140,6 +2142,107 @@ static ssize_t tun_put_user(struct tun_struct *tun,
> return total;
> }
>
> +static struct sk_buff *tun_prepare_xdp_skb(struct sk_buff *skb)
> +{
> + struct sk_buff *nskb;
> +
> + if (skb_shared(skb) || skb_cloned(skb)) {
> + nskb = skb_copy(skb, GFP_ATOMIC);
> + consume_skb(skb);
> + return nskb;
> + }
> +
> + return skb;
> +}
> +
> +static u32 tun_do_xdp_tx_generic(struct tun_struct *tun,
> + struct sk_buff *skb)
> +{
> + struct bpf_prog *xdp_prog;
> + struct xdp_buff xdp;
> + u32 act = XDP_PASS;
> +
> + xdp_prog = rcu_dereference(tun->xdp_egress_prog);
> + if (xdp_prog) {
> + skb = tun_prepare_xdp_skb(skb);
> + if (!skb) {
> + act = XDP_DROP;
> + kfree_skb(skb);
> + goto drop;
> + }
> +
> + act = do_xdp_generic_core(skb, &xdp, xdp_prog);
> + switch (act) {
> + case XDP_TX:
> + /* Rx path generic XDP will be called in this path
> + */
> + local_bh_disable();
> + netif_receive_skb(skb);
> + local_bh_enable();
> + break;
> + case XDP_PASS:
> + break;
> + case XDP_REDIRECT:
> + /* Since we are not handling this case yet, let's free
> + * skb here. In case of XDP_DROP/XDP_ABORTED, the skb
> + * was already freed in do_xdp_generic_core()
> + */
> + kfree_skb(skb);
> + /* fall through */
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + /* fall through */
> + case XDP_ABORTED:
> + trace_xdp_exception(tun->dev, xdp_prog, act);
> + /* fall through */
> + case XDP_DROP:
> + goto drop;
> + }
> + }
> +
> + return act;
> +drop:
> + this_cpu_inc(tun->pcpu_stats->tx_dropped);
> + return act;
> +}
> +
> +static u32 tun_do_xdp_tx(struct tun_struct *tun, struct tun_file *tfile,
> + struct xdp_frame *frame)
> +{
> + struct bpf_prog *xdp_prog;
> + struct xdp_buff xdp;
> + u32 act = XDP_PASS;
> +
> + xdp_prog = rcu_dereference(tun->xdp_egress_prog);
> + if (xdp_prog) {
> + xdp.data_hard_start = frame->data - frame->headroom;
> + xdp.data = frame->data;
> + xdp.data_end = xdp.data + frame->len;
> + xdp.data_meta = xdp.data - frame->metasize;
> +
> + act = bpf_prog_run_xdp(xdp_prog, &xdp);
> + switch (act) {
> + case XDP_PASS:
> + break;
> + case XDP_TX:
> + /* fall through */
> + case XDP_REDIRECT:
> + /* fall through */
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + /* fall through */
> + case XDP_ABORTED:
> + trace_xdp_exception(tun->dev, xdp_prog, act);
> + /* fall through */
> + case XDP_DROP:
> + xdp_return_frame_rx_napi(frame);
> + break;
> + }
> + }
> +
> + return act;
> +}
> +
> static void *tun_ring_recv(struct tun_file *tfile, int noblock, int *err)
> {
> DECLARE_WAITQUEUE(wait, current);
> @@ -2557,6 +2660,52 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
> return ret;
> }
>
> +static int tun_consume_packets(struct tun_file *tfile, void **ptr_array, int n)
> +{
> + void **pkts = tfile->pkt_ptrs;
> + struct xdp_frame *frame;
> + struct tun_struct *tun;
> + int i, num_ptrs;
> + int pkt_cnt = 0;
> + void *ptr;
> + u32 act;
> + int batchsz;
> +
> + if (unlikely(!tfile))
> + return 0;
> +
> + rcu_read_lock();
> + tun = rcu_dereference(tfile->tun);
> + if (unlikely(!tun)) {
> + rcu_read_unlock();
> + return 0;
> + }
> +
> + while (n) {
> + batchsz = (n > MAX_TAP_BATCH) ? MAX_TAP_BATCH : n;
> + n -= batchsz;
> + num_ptrs = ptr_ring_consume_batched(&tfile->tx_ring, pkts,
> + batchsz);
> + if (!num_ptrs)
> + break;
Can't we avoid looping over the packets in the current case
where there are no xdp programs at all?
> + for (i = 0; i < num_ptrs; i++) {
> + ptr = pkts[i];
> + if (tun_is_xdp_frame(ptr)) {
> + frame = tun_ptr_to_xdp(ptr);
> + act = tun_do_xdp_tx(tun, tfile, frame);
> + } else {
> + act = tun_do_xdp_tx_generic(tun, ptr);
> + }
> +
> + if (act == XDP_PASS)
> + ptr_array[pkt_cnt++] = ptr;
> + }
> + }
> +
> + rcu_read_unlock();
> + return pkt_cnt;
> +}
> +
> static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
> int flags)
> {
> @@ -2577,9 +2726,7 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
> ptr = ctl->ptr;
> break;
> case TUN_MSG_CONSUME_PKTS:
> - ret = ptr_ring_consume_batched(&tfile->tx_ring,
> - ctl->ptr,
> - ctl->num);
> + ret = tun_consume_packets(tfile, ctl->ptr, ctl->num);
> goto out;
> case TUN_MSG_UNCONSUME_PKTS:
> ptr_ring_unconsume(&tfile->tx_ring, ctl->ptr,
> --
> 2.21.1 (Apple Git-122.3)
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