netdev - [net v5 2/3] net: sched: add check tc_skip

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Date:   Wed,  8 Dec 2021 22:54:58 +0800
From:   xiangxia.m.yue@...il.com
To:     netdev@...r.kernel.org
Cc:     Tonghao Zhang <xiangxia.m.yue@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Antoine Tenart <atenart@...nel.org>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Wei Wang <weiwan@...gle.com>, Arnd Bergmann <arnd@...db.de>
Subject: [net v5 2/3] net: sched: add check tc_skip_classify in sch egress

From: Tonghao Zhang <xiangxia.m.yue@...il.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@...emloft.net>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <kafai@...com>
Cc: Song Liu <songliubraving@...com>
Cc: Yonghong Song <yhs@...com>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: KP Singh <kpsingh@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Antoine Tenart <atenart@...nel.org>
Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
Cc: Wei Wang <weiwan@...gle.com>
Cc: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.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