netdev - Re: [RFC PATCH 00/12] RCU'ify the net:sched classifier chains

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Date:	Sat, 11 Jan 2014 11:43:13 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	John Fastabend <john.fastabend@...il.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [RFC PATCH 00/12] RCU'ify the net:sched classifier chains

On Fri, Jan 10, 2014 at 1:36 AM, John Fastabend
<john.fastabend@...il.com> wrote:
> There appears to be some interest in a few topics around the qdisc
> layer which could benefit from having the ability to run the
> filters and actions without holding the qdisc lock.
>
> Recently Cong Wang proposed a patch series to drop the ingress
> qdisc and asked for comments. This series I think gets closer to
> that goal.
>
> The ingress qdisc is a simple qdisc which doesn't maintain any
> actual list of skb's and is primarily a hook to attach filters.
> Further the only qdisc that can be attached to the ingress qdisc
> is sch_ingress. The qdisc lock is currently serializing two
> operations (1) tc_classify which is addressed here and (2)
> statistics accounting. The second point is not solved here but
> it could be a matter of making the bstats and qstats per cpu
> stats.


Yeah, actually I tried to make bstats percpu, but I still doubt
if it is necessary, since increasing a 32bit counter doesn't
sound dangerous on SMP?

>
> This is an RFC for now and needs some more work. Some items
> I know about are (a) an audit of the ematch code paths, (b) resolving
> the checpatch errors mostly due to moving code around that
> generates those errors, (c) run smatch, (d) audit u32 code
> for correctness, (e) do a lot more testing so far only very
> basic testing has been done. I tried to put some reasonable
> comments in the commit logs but yes they need more work.
>
> Cong, if its not too much to ask can we use this as a base
> set of patches for this work? I think its reasonably close to
> correct as is.
>

Sure, just that:

1) I myself don't like playing RCU list without using list_head API
it is still hard for me to read.

2) The first patch in your series seems completely irrelevant to
$subject. :)

Thanks.
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