[net v5 2/3] net: sched: add check tc_skip_classify in sch egress

[xiangxia.m.yue@gmail.com]

From: Tonghao Zhang <xiangxia.m.yue@gmail.com>

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. This patch
  is useful when there are a lot of filters with different
  prio. There is ~5 prio in in production, ~1% improvement.

  Rules as below:
  $ for id in $(seq 1 5); do
  $       tc filter add ... egress prio $id ... action mirred egress redirect dev ifb0
  $ done

* 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 ifb.o sec ifb

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 <kafai@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
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 <alexandr.lobakin@intel.com>
Cc: Wei Wang <weiwan@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
---
 net/core/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index a64297a4cc89..81ad415b78f9 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