Re: [Patch v3 net 1/4] net_sched: Implement the right netem duplication behavior

[Cong Wang <xiyou.wangcong@gmail.com>]

On Sun, Jul 13, 2025 at 02:47:45PM -0700, Cong Wang wrote:
> I tested netem packet duplication in two configurations:
> 1. Nest netem-to-netem hierarchy using parent/child attachment
> 2. Single netem using prio qdisc with netem leaf
> 

Below is the complete tcpdump output I had for each of the above setup,
just provide more evidence here since a lot of people don't trust me.

(Don't get me wrong, it is obviously my fault of not being able to gain
trust).


[root@localhost ~]# tcpdump -i lo -nn -c 20 icmp
[  589.079074] lo: entered promiscuous mode
dropped privs to tcpdump
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on lo, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:59:23.485638 IP 127.0.0.1 > 127.0.0.1: ICMP echo request, id 5, seq 1, length 64
12:59:23.485844 IP 127.0.0.1 > 127.0.0.1: ICMP echo request, id 5, seq 1, length 64
12:59:23.486714 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 5, seq 1, length 64
12:59:23.486996 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 5, seq 1, length 64
12:59:23.487867 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 5, seq 1, length 64
12:59:23.488163 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 5, seq 1, length 64


[root@localhost ~]# tcpdump -i lo -nn -c 20 icmp
[  361.831773] lo: entered promiscuous mode
dropped privs to tcpdump
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on lo, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:55:37.074400 IP 127.0.0.1 > 127.0.0.1: ICMP echo request, id 3, seq 1, length 64
12:55:37.074606 IP 127.0.0.1 > 127.0.0.1: ICMP echo request, id 3, seq 1, length 64
12:55:37.074806 IP 127.0.0.1 > 127.0.0.1: ICMP echo request, id 3, seq 1, length 64
12:55:37.075012 IP 127.0.0.1 > 127.0.0.1: ICMP echo request, id 3, seq 1, length 64
12:55:37.076508 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.076789 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.077069 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.077404 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.078825 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.079109 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.079404 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.079927 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.081125 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.081477 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.081763 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.082044 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.083253 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.083534 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.083816 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
12:55:37.084101 IP 127.0.0.1 > 127.0.0.1: ICMP echo reply, id 3, seq 1, length 64
20 packets captured
40 packets received by filter


I didn't include them because the patch description is already very
long. I am happy to add them to the patch description on request.

Please let me know if I miss anything here. I am very very open to
continue iterating this patch.

Thanks!