netdev - Re: [PATCH net v2 1/2] net/sched: Fix backlog accounting in qdisc_dequeue

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Message-ID: <aIPTTxhfC519+cdr@pop-os.localdomain>
Date: Fri, 25 Jul 2025 11:56:15 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: William Liu <will@...lsroot.io>
Cc: netdev@...r.kernel.org, jhs@...atatu.com, pabeni@...hat.com,
	kuba@...nel.org, jiri@...nulli.us, davem@...emloft.net,
	edumazet@...gle.com, horms@...nel.org, savy@...t3mfailure.io
Subject: Re: [PATCH net v2 1/2] net/sched: Fix backlog accounting in
 qdisc_dequeue_internal

On Thu, Jul 24, 2025 at 04:55:27PM +0000, William Liu wrote:
> diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
> index 2a0f3a513bfa..f9e6d76a1712 100644
> --- a/net/sched/sch_fq_codel.c
> +++ b/net/sched/sch_fq_codel.c
> @@ -286,6 +286,10 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
>  	struct fq_codel_flow *flow;
>  	struct list_head *head;
>  
> +	/* reset these here, as change needs them for proper accounting*/
> +	q->cstats.drop_count = 0;
> +	q->cstats.drop_len = 0;
> +
>  begin:
>  	head = &q->new_flows;
>  	if (list_empty(head)) {
> @@ -319,8 +323,6 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
>  	if (q->cstats.drop_count) {
>  		qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
>  					  q->cstats.drop_len);
> -		q->cstats.drop_count = 0;
> -		q->cstats.drop_len = 0;


Is this change really necessary? This could impact more than just the "shrinking
to the limit" code path. We need to minimize the the impact of the patch since it
is targeting -net and -stable.

The rest looks good to me.

Thanks for your patch!