netdev - Re: [PATCH 0/3] Basic deferred TX queue flushing infrastructure.

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Date:	Mon, 25 Aug 2014 19:24:52 -0400
From:	Vlad Yasevich <vyasevic@...hat.com>
To:	David Miller <davem@...emloft.net>, cwang@...pensource.com
CC:	netdev@...r.kernel.org, therbert@...gle.com, jhs@...atatu.com,
	hannes@...essinduktion.org, edumazet@...gle.com,
	jeffrey.t.kirsher@...el.com, rusty@...tcorp.com.au
Subject: Re: [PATCH 0/3] Basic deferred TX queue flushing infrastructure.

On 08/25/2014 06:31 PM, David Miller wrote:
> From: Cong Wang <cwang@...pensource.com>
> Date: Mon, 25 Aug 2014 15:21:00 -0700
> 
>> When I tried to unify the list management of SKB's, I was surprised to see
>> there are still some places relying on skb->next and skb->prev to be
>> the head of the skb struct, since nowadays we have list API's, they still
>> play some magic on these pointers (sctp and tipc IIRC). This is why I
>> gave up, maybe it's time to revise this again.
> 
> I think SCTP should be OK, and yes I do remember that protocol being one of
> the last subsystems making such SKB list pointer assumptions.
> 
> It was using list_*() operations on sk_buff objects or something like that.


All I see that's left is __skb_unlink, __skb_queue_tail and skb_queue_splice_tail_init()

I think you've convert all of them a while ago.

-vlad

> 
>> Talking about skb->next, fortunately we do gso segmentation after
>> going out of qdisc queues, otherwise it's scary to play with these
>> pointers at same time. I think all queues of SKB's are either using
>> just ->next or both ->prev and ->next.
> 
> It occurs to me that perhaps the thing to do is to pass sk_buff ** to
> dev_hard_start_xmit().
> 
> If it really is important to free the original GSO skb after the
> segmented parts, we can run that as part of the destructor of the
> final segment.
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