netdev - Re: [PATCH net-next v2] fq_codel: generalise ce_threshold marking for subset of traffic

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Date:   Wed, 20 Oct 2021 09:20:32 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org, edumazet@...gle.com
Subject: Re: [PATCH net-next v2] fq_codel: generalise ce_threshold marking for
 subset of traffic



On 10/19/21 10:47 AM, Toke Høiland-Jørgensen wrote:
> The commit in the Fixes tag expanded the ce_threshold feature of FQ-CoDel
> so it can be applied to a subset of the traffic, using the ECT(1) bit of
> the ECN field as the classifier. However, hard-coding ECT(1) as the only
> classifier for this feature seems limiting, so let's expand it to be more
> general.
> 
> To this end, change the parameter from a ce_threshold_ect1 boolean, to a
> one-byte selector/mask pair (ce_threshold_{selector,mask}) which is applied
> to the whole diffserv/ECN field in the IP header. This makes it possible to
> classify packets by any value in either the ECN field or the diffserv
> field. In particular, setting a selector of INET_ECN_ECT_1 and a mask of
> INET_ECN_MASK corresponds to the functionality before this patch, and a
> mask of ~INET_ECN_MASK allows using the selector as a straight-forward
> match against a diffserv code point:
> 
>  # apply ce_threshold to ECT(1) traffic
>  tc qdisc replace dev eth0 root fq_codel ce_threshold 1ms ce_threshold_selector 0x1/0x3
> 
>  # apply ce_threshold to ECN-capable traffic marked as diffserv AF22
>  tc qdisc replace dev eth0 root fq_codel ce_threshold 1ms ce_threshold_selector 0x50/0xfc
> 
> Regardless of the selector chosen, the normal rules for ECN-marking of
> packets still apply, i.e., the flow must still declare itself ECN-capable
> by setting one of the bits in the ECN field to get marked at all.
> 
> v2:
> - Add tc usage examples to patch description
> 
> Fixes: e72aeb9ee0e3 ("fq_codel: implement L4S style ce_threshold_ect1 marking")
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

BTW, the Fixes: tag seems not really needed, your patch is a followup/generalization.