netdev - Re: [PATCH net v6 1/2] net/sched: sch_cake: Fix incorrect qlen reduction in cake

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Message-ID: <aSaCiO/+zrzk9eF1@pop-os.localdomain>
Date: Tue, 25 Nov 2025 20:31:04 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: Xiang Mei <xmei5@....edu>
Cc: security@...nel.org, netdev@...r.kernel.org, toke@...e.dk,
	cake@...ts.bufferbloat.net, bestswngs@...il.com
Subject: Re: [PATCH net v6 1/2] net/sched: sch_cake: Fix incorrect qlen
 reduction in cake_drop

On Tue, Nov 25, 2025 at 03:02:12PM -0700, Xiang Mei wrote:
> @@ -1927,24 +1928,30 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>  	if (q->buffer_used > q->buffer_max_used)
>  		q->buffer_max_used = q->buffer_used;
>  
> -	if (q->buffer_used > q->buffer_limit) {
> -		bool same_flow = false;
> -		u32 dropped = 0;
> -		u32 drop_id;
> +	if (q->buffer_used <= q->buffer_limit)
> +		return NET_XMIT_SUCCESS;
>  
> -		while (q->buffer_used > q->buffer_limit) {
> -			dropped++;
> -			drop_id = cake_drop(sch, to_free);
> +	prev_qlen = sch->q.qlen;
> +	prev_backlog = sch->qstats.backlog;
>  
> -			if ((drop_id >> 16) == tin &&
> -			    (drop_id & 0xFFFF) == idx)
> -				same_flow = true;
> -		}
> -		b->drop_overlimit += dropped;
> +	while (q->buffer_used > q->buffer_limit) {
> +		drop_id = cake_drop(sch, to_free);
> +		if ((drop_id >> 16) == tin &&
> +		    (drop_id & 0xFFFF) == idx)
> +			same_flow = true;
> +	}
> +
> +	/* Compute the droppped qlen and pkt length */

Just a nit: this comment is not needed, because the code below is
readable enough to explain itself. :)


Regards,
Cong Wang