netdev - Re: [PATCH] net/sched: netem: account for backlog updates from child qdisc

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Message-ID: <20241202191312.3d3c8097@kernel.org>
Date: Mon, 2 Dec 2024 19:13:12 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Martin Ottens <martin.ottens@....de>
Cc: Stephen Hemminger <stephen@...workplumber.org>, Jamal Hadi Salim
 <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko
 <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/sched: netem: account for backlog updates from
 child qdisc

On Tue, 26 Nov 2024 00:18:25 +0100 Martin Ottens wrote:
> @@ -702,8 +706,8 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
>  tfifo_dequeue:
>  	skb = __qdisc_dequeue_head(&sch->q);
>  	if (skb) {
> -		qdisc_qstats_backlog_dec(sch, skb);
>  deliver:
> +		qdisc_qstats_backlog_dec(sch, skb);
>  		qdisc_bstats_update(sch, skb);
>  		return skb;
>  	}

Isn't this sort of a change all we need?
I don't understand why we need to perform packet accounting 
in a separate new member (t_len). You seem to fix qlen accounting,
anyway, and I think sch->limit should apply to the qdisc and all
its children. Not just qdisc directly (since most classful qdiscs
don't hold packets).

I'm not a qdisc expert, so if you feel confident about this code you
need to explain the thinking in the commit message..
-- 
pw-bot: cr