netdev - Re: [PATCH net-next 2/2] net: sched: do not acquire qdisc spinlock in qdisc/class stats dump

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Date:	Tue, 7 Jun 2016 16:39:20 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	"David S . Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	John Fastabend <john.fastabend@...il.com>,
	Kevin Athey <kda@...gle.com>,
	Xiaotian Pei <xiaotian@...gle.com>
Subject: Re: [PATCH net-next 2/2] net: sched: do not acquire qdisc spinlock in
 qdisc/class stats dump

On Mon, Jun 6, 2016 at 4:53 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Really sounds overkill to care about these, as probably no one needs to
> get a 'consistent view of all these counters in a snapshot'.
>
> Even as of today, the qlen/backlog pair is wrong. No one ever used these
> values in an SNMP agent.
>
> Note that qlen/backlog is changed both by enqueue/dequeue, so the
> seqcount protection would not work.

I see.

>
> With the percpu stats thing, stats can not be fetched in a 'consistent'
> way.

Fair enough.

Thanks!