netdev - Re: [RFC Patch net-next] net_sched: make classifying lockless on ingress

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Date:	Fri, 20 Dec 2013 18:32:49 -0800
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [RFC Patch net-next] net_sched: make classifying lockless on
 ingress

On 12/20/2013 4:24 PM, Cong Wang wrote:
> On Fri, Dec 20, 2013 at 4:08 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Fri, 2013-12-20 at 15:57 -0800, Cong Wang wrote:
>>
>>> Just push the lock down to ->enqueue() ? Since ingress qdisc is classless
>>> and its ->dequeue() is nop.
>>
>>
>> https://github.com/jrfastab/Linux-Kernel-QOS
>>
>> https://github.com/jrfastab/Linux-Kernel-QOS/commit/67746f95acd77cf15d7ce34f644b76058ce19813
>>
>
> It's a nice idea to introduce a ->prequeue().
>
> And so brave to play with RCU on singly linked list... maybe I can
> just steal the ->prequeue() piece. John? :-D

If you only steal the prequeue piece then you don't solve the lock
contention part so I don't think it helps. At which point I suspect
you might as well use one of the existing qdiscs not designed for
multiqueue nics.

>
> BTW, the last commit is about 5 months ago...

Yeah well I imagined I would write a rate limiting qdisc to use
this infrastructure. Jamal hinted at using a systolic processes
for this. But I work on this when I have time and have been
busy the last few months with other things unfortunately.

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