netdev - Re: [PATCH v5 net-next 15/15] tcp: try to avoid safer when ACKs are thinned

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Message-ID: <298cfc4c-3818-4c6e-9348-4b1aff00e96c@redhat.com>
Date: Tue, 29 Apr 2025 16:11:40 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: 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@...ia-bell-labs.com,
 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@...le.com
Subject: Re: [PATCH v5 net-next 15/15] tcp: try to avoid safer when ACKs are
 thinned

On 4/22/25 5:36 PM, chia-yu.chang@...ia-bell-labs.com wrote:
> From: Ilpo Järvinen <ij@...nel.org>
> 
> Add newly acked pkts EWMA. When ACK thinning occurs, select
> between safer and unsafe cep delta in AccECN processing based
> on it. If the packets ACKed per ACK tends to be large, don't
> conservatively assume ACE field overflow.
> 
> Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> ---
>  include/linux/tcp.h  |  1 +
>  net/ipv4/tcp.c       |  4 +++-
>  net/ipv4/tcp_input.c | 20 +++++++++++++++++++-
>  3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index b93bf1785008..99ca0b8435c8 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -315,6 +315,7 @@ struct tcp_sock {
>  		est_ecnfield:2;/* ECN field for AccECN delivered estimates */
>  	u32	app_limited;	/* limited until "delivered" reaches this val */
>  	u64	accecn_opt_tstamp;	/* Last AccECN option sent timestamp */
> +	u16	pkts_acked_ewma;/* Pkts acked EWMA for AccECN cep heuristic */

It looks like this field is accessed only on the RX path and does not
belong to this cacheline group.

/P