Re: [PATCH v3 net-next 1/4] net: implement support for low latencysocket polling

[Pekka Riikonen]

On Tue, 21 May 2013, David Miller wrote:

> From: Pekka Riikonen <priikone@xxxxxx>
> Date: Tue, 21 May 2013 19:02:19 +0200 (CEST)
>
> > On Tue, 21 May 2013, Eric Dumazet wrote:
> >
> > : > > Alternatively, use a napi_id instead of a pointer.
> > : >
> > : > I'm not sure I understand what you propose.
> > :
> > : Oh well.
> > :
> > : To get a pointer to a struct net_device, we can use ifindex, and do a
> > : rcu lookup into a hash table to get the net_device. We do not need
> > : {pointer,ifindex} but {ifindex} is enough
> > :
> > : My suggestion is to not have skb->skb_ref but skb->napi_index : Its safe
> > : to copy its value from skb->napi_index to sk->napi_index without
> > : refcounting.
> > :
> > : All NAPI need to get a unique napi_index, and be inserted in a hash
> > : table for immediate/fast lookup.
> > :
> > Maybe even that's not needed.  Couldn't skb->queue_mapping give the
> > correct NAPI instance in multiqueue nics?  The NAPI instance could be made
> > easily available from skb->dev.  In any case an index is much better than
> > a new pointer.
>
> Queue mapping is more volatile, and consider layered devices.
Yes, true.  The napi_index then is probably the way to go.  Main thing for 
me is that it doesn't increase skb size when in union with dma_cookie (skb 
has been growing lately).

	Pekka

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