netdev - Re: [PATCH net-next] tcp: get rid of sysctl_tcp_adv_win

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Date: Thu, 20 Jul 2023 17:41:32 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>,  Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, Soheil Hassas Yeganeh <soheil@...gle.com>, Neal
 Cardwell <ncardwell@...gle.com>, Yuchung Cheng <ycheng@...gle.com>,
 eric.dumazet@...il.com
Subject: Re: [PATCH net-next] tcp: get rid of sysctl_tcp_adv_win_scale

Hi,

On Mon, 2023-07-17 at 15:29 +0000, Eric Dumazet wrote:
> +static inline void tcp_scaling_ratio_init(struct sock *sk)
> +{
> +	/* Assume a conservative default of 1200 bytes of payload per 4K page.
> +	 * This may be adjusted later in tcp_measure_rcv_mss().
> +	 */
> +	tcp_sk(sk)->scaling_ratio = (1200 << TCP_RMEM_TO_WIN_SCALE) /
> +				    SKB_TRUESIZE(4096);

I'm giving this patch a closer look because mptcp_rcv_space_adjust
needs to be updated on top of it. Should SKB_TRUESIZE(4096) be replaced
with:

4096 + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) 

to be more accurate? The page should already include the shared info,
right?

Likely not very relevant as the ratio is updated to a more accurate
value with the first packet, mostly to try to understand the code
correctly.

Thanks!

Paolo