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

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Date:	Mon, 25 Aug 2014 22:45:19 +0000
From:	Jon Maloy <jon.maloy@...csson.com>
To:	David Miller <davem@...emloft.net>,
	"cwang@...pensource.com" <cwang@...pensource.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"therbert@...gle.com" <therbert@...gle.com>,
	"jhs@...atatu.com" <jhs@...atatu.com>,
	"hannes@...essinduktion.org" <hannes@...essinduktion.org>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"jeffrey.t.kirsher@...el.com" <jeffrey.t.kirsher@...el.com>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>
Subject: RE: [PATCH 0/3] Basic deferred TX queue flushing infrastructure.



> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of David Miller
> Sent: August-25-14 6:32 PM
> To: 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.
> 
> 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

I am not aware of any such assumptions in TIPC.  For me you can go ahead
with this.

Regards
///jon


> > 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.
> 
> > 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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