netdev - [net v3 2/3] net: sched: add check tc_skip

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Date:   Mon, 29 Nov 2021 12:55:02 +0800
From:   xiangxia.m.yue@...il.com
To:     netdev@...r.kernel.org
Cc:     Tonghao Zhang <xiangxia.m.yue@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        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>,
        Björn Töpel <bjorn@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [net v3 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.

  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@...gle.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>
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: "Björn Töpel" <bjorn@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
---
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