Re: [PATCH net-next] net: inline eth_type_trans() fast path

[Eric Dumazet <edumazet@kernel.org>]

On Thu, Oct 1, 2026 at 5:58 PM Alexander Lobakin
<aleksander.lobakin@intel.com> wrote:
>
> From: Edumazet@kernel.org <edumazet@kernel.org>
> Date: Wed, 30 Sep 2026 19:29:57 +0200
>
> > eth_type_trans() is called once per received packet by most
> > Ethernet drivers, and by core helpers (napi_gro_frags(),
> > xdp_build_skb_from_*(), veth, tun, tunnels, loopback...).
> >
> > With CONFIG_MITIGATION_RETHUNK / SRSO, the call and return
> > are not free anymore.
> >
> > Add eth_type_trans_inline(), handling the common case inline:
> > unicast frame sent to dev->dev_addr, with a real ethertype,
> > on a device which is not a DSA conduit. All other frames
> > (multicast, broadcast, otherhost, 802.2, runts, DSA)
> > are handled by the out-of-line eth_type_trans().
> >
> > eth_type_trans() is now a macro calling eth_type_trans_inline(),
> > so that all existing callers get the fast path. The out-of-line
> > version remains exported, and can be called with
> > (eth_type_trans)(skb, dev). bpf_prog_test_run_skb() uses this
>
> Shouldn't it get renamed to e.g. eth_type_trans_slow() to avoid this
> confusion?

This was my initial idea, but this would make the patch a bit more
invasive and touch bpf selftests, something like:

Let me know if I should send a V2 and CC bpf maintainers, thanks!

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 513354e928cb58f837fdc93a77f2e896de1ef916..8f4e9dd18001a4c32455fefd74fe38db270756d1
100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1165,7 +1165,8 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog,
const union bpf_attr *kattr,
                        goto out;
                }
        }
-       skb->protocol = eth_type_trans(skb, dev);
+       /* Always call the out-of-line version, for fentry/fexit selftests. */
+       skb->protocol = eth_type_trans_slow(skb, dev);
        skb_reset_network_header(skb);

        switch (skb->protocol) {
diff --git a/tools/testing/selftests/bpf/progs/core_kern.c
b/tools/testing/selftests/bpf/progs/core_kern.c
index 004f2acef2eb0b0d80184423a3e8ba399feee1f3..fca26af98a7b92898a4adfde19f63b342f29db74
100644
--- a/tools/testing/selftests/bpf/progs/core_kern.c
+++ b/tools/testing/selftests/bpf/progs/core_kern.c
@@ -47,14 +47,14 @@ int BPF_PROG(tp_xdp_devmap_xmit_multi, const
struct net_device
        return randmap(from_dev->ifindex, from_dev);
 }

-SEC("fentry/eth_type_trans")
+SEC("fentry/eth_type_trans_slow")
 int BPF_PROG(fentry_eth_type_trans, struct sk_buff *skb,
             struct net_device *dev, unsigned short protocol)
 {
        return randmap(dev->ifindex + skb->len, dev);
 }

-SEC("fexit/eth_type_trans")
+SEC("fexit/eth_type_trans_slow")
 int BPF_PROG(fexit_eth_type_trans, struct sk_buff *skb,
             struct net_device *dev, unsigned short protocol)
 {
diff --git a/tools/testing/selftests/bpf/progs/kfree_skb.c
b/tools/testing/selftests/bpf/progs/kfree_skb.c
index 7236da72ce8055f9a0165d3b4334a04d17d110b8..678c15c151944b44e276cf1280c77cb436ff7b10
100644
--- a/tools/testing/selftests/bpf/progs/kfree_skb.c
+++ b/tools/testing/selftests/bpf/progs/kfree_skb.c
@@ -114,7 +114,7 @@ struct {
        bool fexit_test_ok;
 } result = {};

-SEC("fentry/eth_type_trans")
+SEC("fentry/eth_type_trans_slow")
 int BPF_PROG(fentry_eth_type_trans, struct sk_buff *skb, struct
net_device *dev,
             unsigned short protocol)
 {
@@ -132,7 +132,7 @@ int BPF_PROG(fentry_eth_type_trans, struct sk_buff
*skb, struct net_device *dev,
        return 0;
 }

-SEC("fexit/eth_type_trans")
+SEC("fexit/eth_type_trans_slow")
 int BPF_PROG(fexit_eth_type_trans, struct sk_buff *skb, struct net_device *dev,
             unsigned short protocol)
 {