linux-kernel - Re: [PATCH v3 net-next 1/4] net: implement support for low latency socket polling

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Date:	Tue, 21 May 2013 12:29:56 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Cc:	Pekka Riikonen <priikone@....fi>,
	Dave Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Willem de Bruijn <willemb@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v3 net-next 1/4] net: implement support for low latency
 socket polling

On Tue, 2013-05-21 at 22:25 +0300, Eliezer Tamir wrote:
> On 21/05/2013 20:51, Eric Dumazet wrote:
> > On Tue, 2013-05-21 at 10:48 -0700, Eric Dumazet wrote:
> >
> >> We do not keep skb->dev information once a packet leaves the rcu
> >> protected region.
> >>
> >> Once packet is queued to tcp input queues, skb->dev is NULL.
> >
> > This is done in tcp_v4_rcv() & tcp_v6_rcv()
> 
> So if we move calling sk_mark_ll() into the rcu protected region,
> We would not need the gen id in the skb.
> We could save skb->dev and skb->queue_mapping along with the generation 
> id in the socket.
> 
> then we don't need to change the skb struct at all.
> skb_mark_ll() can go away.
> we also call sk_mark_ll in one central place in net_protocol->handler 
> instead of all over the place.
> 
> or am I missing something?


You cannot keep a pointer to some object without taking a reference on
the object.

Thats why I suggested to use an napi identifier instead, this is safe
and cheap.



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