netdev - Re: [PATCH net-next 00/10] net_sched: speedup qdisc dequeue

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Message-ID: <20251110092736.5642f227@kernel.org>
Date: Mon, 10 Nov 2025 09:27:36 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Paolo Abeni
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Jamal Hadi Salim
 <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko
 <jiri@...nulli.us>, Toke Høiland-Jørgensen
 <toke@...hat.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, Willem de Bruijn
 <willemb@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 00/10] net_sched: speedup qdisc dequeue

On Mon, 10 Nov 2025 09:15:46 -0800 Eric Dumazet wrote:
> On Mon, Nov 10, 2025 at 8:44 AM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Mon, 10 Nov 2025 09:44:55 +0000 Eric Dumazet wrote:  
> > > Avoid up to two cache line misses in qdisc dequeue() to fetch
> > > skb_shinfo(skb)->gso_segs/gso_size while qdisc spinlock is held.
> > >
> > > Idea is to cache gso_segs at enqueue time before spinlock is
> > > acquired, in the first skb cache line, where we already
> > > have qdisc_skb_cb(skb)->pkt_len.
> > >
> > > This series gives a 8 % improvement in a TX intensive workload.
> > >
> > > (120 Mpps -> 130 Mpps on a Turin host, IDPF with 32 TX queues)  
> >
> > According to CI this breaks a bunch of tests.
> >
> > https://netdev.bots.linux.dev/contest.html?branch=net-next-2025-11-10--12-00
> >
> > I think they all hit:
> >
> > [   20.682474][  T231] WARNING: CPU: 3 PID: 231 at ./include/net/sch_generic.h:843 __dev_xmit_skb+0x786/0x1550  
> 
> Oh well, I will add this in V2, thank you !
> 
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index b76436ec3f4aa412bac1be3371f5c7c6245cc362..79501499dafba56271b9ebd97a8f379ffdc83cac
> 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -841,7 +841,7 @@ static inline unsigned int qdisc_pkt_segs(const
> struct sk_buff *skb)
>         u32 pkt_segs = qdisc_skb_cb(skb)->pkt_segs;
> 
>         DEBUG_NET_WARN_ON_ONCE(pkt_segs !=
> -                              skb_is_gso(skb) ? skb_shinfo(skb)->gso_segs : 1);
> +                       (skb_is_gso(skb) ? skb_shinfo(skb)->gso_segs : 1));
>         return pkt_segs;
>  }

Hm, I think we need more..

The non-debug workers are also failing and they have DEBUG_NET=n

Looks like most of the non-debug tests are tunnel and bridge related.
VxLAN, GRE etc. 

https://netdev.bots.linux.dev/contest.html?pass=0&branch=net-next-2025-11-10--12-00&executor=vmksft-forwarding