netdev - Re: [PATCH RFC] net_sched/codel: do not defer queue length update

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Message-ID: <efdb1e4a-6c7e-a0ed-059b-cb2eb7b1c92c@nbd.name>
Date:   Sun, 11 Mar 2018 08:58:25 +0100
From:   Felix Fietkau <nbd@....name>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH RFC] net_sched/codel: do not defer queue length update

On 2017-08-21 10:14, Konstantin Khlebnikov wrote:
> When codel wants to drop last packet in ->dequeue() it cannot call
> qdisc_tree_reduce_backlog() right away - it will notify parent qdisc
> about zero qlen and HTB/HFSC will deactivate class. The same class will
> be deactivated second time by caller of ->dequeue(). Currently codel and
> fq_codel defer update. This triggers warning in HFSC when it's qlen != 0
> but there is no active classes.
> 
> This patch update parent queue length immediately: just temporary increase
> qlen around qdisc_tree_reduce_backlog() to prevent first class deactivation
> if we have skb to return.
> 
> This might open another problem in HFSC - now operation peek could fail and
> deactivate parent class.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=109581
This has been tested by several people and it seems to be working well.
Please make sure this gets merged soon.

Thanks,

- Felix