netdev - Re: [PATCH net-next] sched: add dualpi2 scheduler module

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Date:   Mon, 11 Mar 2019 08:41:23 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Olga Albisser <olgabnd@...il.com>, netdev@...r.kernel.org
Cc:     Olga Albisser <olga@...isser.org>,
        Koen De Schepper <koen.de_schepper@...ia-bell-labs.com>,
        Oliver Tilmans <olivier.tilmans@...ia-bell-labs.com>,
        Bob Briscoe <research@...briscoe.net>,
        Henrik Steen <henrist@...rist.net>
Subject: Re: [PATCH net-next] sched: add dualpi2 scheduler module

FYI, net-next tree is currently closed.

On 03/11/2019 08:14 AM, Olga Albisser wrote:
> DUALPI2 provides extremely low latency & loss to traffic that uses a
> scalable congestion controller (e.g. L4S, DCTCP) without degrading the
> performance of 'classic' traffic (e.g. Reno, Cubic etc.). It is intended
> to be the reference implementation of the IETF's DualQ Coupled AQM.


> +
> +static int dualpi2_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> +				 struct sk_buff **to_free)
> +{
> +	struct dualpi2_sched_data *q = qdisc_priv(sch);
> +	u32 ecn = get_ecn_field(skb);
> +	int err;
> +
> +	/* set to the time the HTQ packet is in the Q */
> +	__net_timestamp(skb);
> +

You can not do that in a qdisc ( blindly overwriting skb->tstamp )

EDT model was adopted in TCP in linux-4.20

You will need to use part of skb->cb instead.

BTW, prefer CLOCK_MONOTONIC, this can avoid all sort of surprises...