[net v3 2/3] net: sched: add check tc_skip_classify in sch egress

From: Tonghao Zhang <redacted>

Try to resolve the issues as below:
* We look up and then check tc_skip_classify flag in net
  sched layer, even though skb don't want to be classified.
  That case may consume a lot of cpu cycles.

  Install the rules as below:
  $ for id in $(seq 1 100); do
  $       tc filter add ... egress prio $id ... action mirred egress redirect dev ifb0
  $ done

  netperf:
  $ taskset -c 1 netperf -t TCP_RR -H ip -- -r 32,32
  $ taskset -c 1 netperf -t TCP_STREAM -H ip -- -m 32

  Before: 10662.33 tps, 108.95 Mbit/s
  After:  12434.48 tps, 145.89 Mbit/s
  For TCP_RR, there are 16.6% improvement, TCP_STREAM 33.9%.

* bpf_redirect may be invoked in egress path. if we don't
  check the flags and then return immediately, the packets
  will loopback.

  $ tc filter add dev eth0 egress bpf direct-action obj \
	  test_tc_redirect_ifb.o sec redirect_ifb

Cc: Willem de Bruijn <willemb@google.com>
Cc: Cong Wang <redacted>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <redacted>
Cc: Song Liu <redacted>
Cc: Yonghong Song <redacted>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Antoine Tenart <atenart@kernel.org>
Cc: Alexander Lobakin <redacted>
Cc: Wei Wang <redacted>
Cc: "Björn Töpel" <bjorn@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tonghao Zhang <redacted>
---
v2: https://patchwork.kernel.org/project/netdevbpf/patch/20211103143208.41282-1-xiangxia.m.yue@gmail.com/
Willem de Bruijn and Daniel Borkmann, comment this patch, but I think we should fix this,
bpf_redirect may also loopback the packets. I hope there are more comments?
---
 net/core/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 823917de0d2b..4ceb927b1577 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -3823,6 +3823,9 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 	if (!miniq)
 		return skb;
 
+	if (skb_skip_tc_classify(skb))
+		return skb;
+
 	/* qdisc_skb_cb(skb)->pkt_len was already set by the caller. */
 	qdisc_skb_cb(skb)->mru = 0;
 	qdisc_skb_cb(skb)->post_ct = false;

-- 
2.27.0