netdev - Re: [PATCH v5 net-next 01/14] tcp: try to avoid safer when ACKs are thinned

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Message-ID: <2f38933e-f24e-4a14-a906-0d06bc194a21@redhat.com>
Date: Thu, 6 Nov 2025 11:57:09 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, edumazet@...gle.com, parav@...dia.com,
 linux-doc@...r.kernel.org, corbet@....net, horms@...nel.org,
 dsahern@...nel.org, kuniyu@...gle.com, bpf@...r.kernel.org,
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 Jason_Livingood@...cast.com, vidhi_goel@...le.com
Subject: Re: [PATCH v5 net-next 01/14] tcp: try to avoid safer when ACKs are
 thinned

On 10/30/25 3:34 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.
> 
> This patch uses the existing 2-byte holes in the rx group for new
> u16 variables withtout creating more holes. Below are the pahole
> outcomes before and after this patch:
> 
> [BEFORE THIS PATCH]
> struct tcp_sock {
>     [...]
>     u32                        delivered_ecn_bytes[3]; /*  2744    12 */
>     /* XXX 4 bytes hole, try to pack */
> 
>     [...]
>     __cacheline_group_end__tcp_sock_write_rx[0];       /*  2816     0 */
> 
>     [...]
>     /* size: 3264, cachelines: 51, members: 177 */
> }
> 
> [AFTER THIS PATCH]
> struct tcp_sock {
>     [...]
>     u32                        delivered_ecn_bytes[3]; /*  2744    12 */
>     u16                        pkts_acked_ewma;        /*  2756     2 */
>     /* XXX 2 bytes hole, try to pack */
> 
>     [...]
>     __cacheline_group_end__tcp_sock_write_rx[0];       /*  2816     0 */
> 
>     [...]
>     /* size: 3264, cachelines: 51, members: 178 */
> }
> 
> Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> Co-developed-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>

Acked-by: Paolo Abeni <pabeni@...hat.com>