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

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Date:	Fri, 20 Dec 2013 15:57:22 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	John Fastabend <john.r.fastabend@...el.com>
Subject: Re: [RFC Patch net-next] net_sched: make classifying lockless on ingress

On Fri, Dec 20, 2013 at 3:49 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2013-12-20 at 15:28 -0800, Cong Wang wrote:
>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index c482fe8..7cc0d6a 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -3382,10 +3382,8 @@ static int ing_filter(struct sk_buff *skb, struct netdev_queue *rxq)
>>
>>       q = rxq->qdisc;
>>       if (q != &noop_qdisc) {
>> -             spin_lock(qdisc_lock(q));
>>               if (likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
>>                       result = qdisc_enqueue_root(skb, q);
>> -             spin_unlock(qdisc_lock(q));
>>       }
>>
>
> Well... That would be too easy.
>
> Really, a lot more work would be needed.
>
> Qdisc ->enqueue()/dequeue()/reset()/... all assume the qdisc lock is
> held.

Just push the lock down to ->enqueue() ? Since ingress qdisc is classless
and its ->dequeue() is nop.


>
> John Fastabend did some work on this area.
>


Thanks.
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