netdev - RE: [PATCH v6 net-next 04/15] tcp: AccECN core

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Message-ID:
 <PAXPR07MB7984C02A5B910446670F056AA391A@PAXPR07MB7984.eurprd07.prod.outlook.com>
Date: Wed, 14 May 2025 13:53:23 +0000
From: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
To: Paolo Abeni <pabeni@...hat.com>, "horms@...nel.org" <horms@...nel.org>,
	"dsahern@...nel.org" <dsahern@...nel.org>, "kuniyu@...zon.com"
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	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "dave.taht@...il.com"
	<dave.taht@...il.com>, "jhs@...atatu.com" <jhs@...atatu.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "stephen@...workplumber.org"
	<stephen@...workplumber.org>, "xiyou.wangcong@...il.com"
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	"davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
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	"ncardwell@...gle.com" <ncardwell@...gle.com>, "Koen De Schepper (Nokia)"
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	"Jason_Livingood@...cast.com" <Jason_Livingood@...cast.com>, vidhi_goel
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CC: "Olivier Tilmans (Nokia)" <olivier.tilmans@...ia.com>
Subject: RE: [PATCH v6 net-next 04/15] tcp: AccECN core

> -----Original Message-----
> From: Paolo Abeni <pabeni@...hat.com> 
> Sent: Tuesday, May 13, 2025 3:55 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>; horms@...nel.org; dsahern@...nel.org; kuniyu@...zon.com; bpf@...r.kernel.org; netdev@...r.kernel.org; dave.taht@...il.com; jhs@...atatu.com; kuba@...nel.org; stephen@...workplumber.org; xiyou.wangcong@...il.com; jiri@...nulli.us; davem@...emloft.net; edumazet@...gle.com; andrew+netdev@...n.ch; donald.hunter@...il.com; ast@...erby.net; liuhangbin@...il.com; shuah@...nel.org; linux-kselftest@...r.kernel.org; ij@...nel.org; ncardwell@...gle.com; Koen De Schepper (Nokia) <koen.de_schepper@...ia-bell-labs.com>; g.white <g.white@...lelabs.com>; ingemar.s.johansson@...csson.com; mirja.kuehlewind@...csson.com; cheshire@...le.com; rs.ietf@....at; Jason_Livingood@...cast.com; vidhi_goel <vidhi_goel@...le.com>
> Cc: Olivier Tilmans (Nokia) <olivier.tilmans@...ia.com>
> Subject: Re: [PATCH v6 net-next 04/15] tcp: AccECN core
> 
> 
> CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
> 
> 
> 
> On 5/9/25 11:18 PM, chia-yu.chang@...ia-bell-labs.com wrote:
> > @@ -5098,7 +5100,8 @@ static void __init tcp_struct_check(void)
> >       /* 32bit arches with 8byte alignment on u64 fields might need padding
> >        * before tcp_clock_cache.
> >        */
> > -     CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 92 + 4);
> > +     CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, 
> > + tcp_sock_write_txrx, 96 + 4);
> 
> This looks inconsistent with the pahole output in the commit message (the groups looks 95 bytes wide, comprising the holes)

Hi Paolo,

Thanks for the feedback.
Indeed, the group size shall be updated before adding AccECN changes based on pahole results.
And I will fix in #3, #4, #6 for tcp_sock_write_txrx, #3 for tcp_sock_write_tx, and #10 for tcp_sock_write_rx.
 
> [...]
> > @@ -382,11 +393,17 @@ static void tcp_ecn_send(struct sock *sk, struct 
> > sk_buff *skb,  {
> >       struct tcp_sock *tp = tcp_sk(sk);
> >
> > -     if (tcp_ecn_mode_rfc3168(tp)) {
> > +     if (!tcp_ecn_mode_any(tp))
> > +             return;
> > +
> > +     INET_ECN_xmit(sk);
> > +     if (tcp_ecn_mode_accecn(tp)) {
> > +             tcp_accecn_set_ace(th, tp);
> > +             skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN;
> > +     } else {
> >               /* Not-retransmitted data segment: set ECT and inject CWR. */
> >               if (skb->len != tcp_header_len &&
> >                   !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
> > -                     INET_ECN_xmit(sk);
> 
> The above chunk apparently changes the current behaviour for !tcp_ecn_mode_accecn(), unconditionally setting ECN, while before ECN was set only for non retrans segments.
> 
> /P

This will be fixed in the next version.

Chia-Yu