netdev - Re: [PATCH net-next v14 3/7] sch_cake: Add optional ACK filter

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Date:   Mon, 21 May 2018 14:15:11 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>,
        netdev@...r.kernel.org, cake@...ts.bufferbloat.net
Cc:     Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next v14 3/7] sch_cake: Add optional ACK filter



On 05/21/2018 01:35 PM, Toke Høiland-Jørgensen wrote:

> +
> +	/* 3 reserved flags must be unset to avoid future breakage
> +	 * ECE/CWR/NS can be safely ignored
> +	 * ACK must be set
> +	 * All other flags URG/PSH/RST/SYN/FIN must be unset
> +	 * 0x0FFF0000 = all TCP flags (confirm ACK=1, others zero)
> +	 * 0x01C00000 = NS/CWR/ECE (safe to ignore)
> +	 * 0x0E3F0000 = 0x0FFF0000 & ~0x01C00000
> +	 */
> +	if (((tcp_flag_word(tcph) &
> +	      cpu_to_be32(0x0E3F0000)) != TCP_FLAG_ACK))
> +		return false;
>


Why ECE/CWR/NS can be ignored ?

DCTCP would disagree, and maybe BBR soon.