netdev - Re: [RFC PATCH 10/13] net: sched: lockless support for netif

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Date:	Wed, 17 Aug 2016 12:46:29 -0700
From:	John Fastabend <john.fastabend@...il.com>
To:	xiyou.wangcong@...il.com, jhs@...atatu.com,
	alexei.starovoitov@...il.com, eric.dumazet@...il.com,
	brouer@...hat.com
Cc:	john.r.fastabend@...el.com, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [RFC PATCH 10/13] net: sched: lockless support for netif_schedule

On 16-08-17 12:37 PM, John Fastabend wrote:
> netif_schedule uses a bit QDISC_STATE_SCHED to tell the qdisc layer
> if a run of the qdisc has been scheduler. This is important when
> tearing down qdisc instances. We can rcu_free an instance for example
> if its possible that we might have outstanding references to it.
> 
> Perhaps more importantly in the per cpu lockless case we need to
> schedule a run of the qdisc on all qdiscs that are enqueu'ing packets
> and hitting the gso_skb requeue logic or else the skb may get stuck
> on the gso_skb queue without anything to finish the xmit.
> 
> This patch uses a reference counter instead of a bit to account for
> the multiple CPUs.
> ---

oops the commit message is incorrect here it actually uses a per cpu
state bitmask to track this.