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Date: Fri, 24 Jan 2020 22:36:11 +0900
From: Prashant Bhole <bholeprashant.oss@...il.com>
To: "Michael S. Tsirkin" <mst@...hat.com>,
David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org, 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, Prashant Bhole <prashantbhole.linux@...il.com>
Subject: Re: [PATCH bpf-next 10/12] tun: run XDP program in tx path
On 1/23/2020 5:23 PM, Michael S. Tsirkin wrote:
> 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?
That's doable. Thanks.
Prashant
>
>
>> + 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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