Messages in this thread | | | Subject | Re: [PATCH v3 net-next 1/4] net: implement support for low latency socket polling | From | Eric Dumazet <> | Date | Tue, 21 May 2013 06:28:46 -0700 |
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On Tue, 2013-05-21 at 10:28 +0300, Eliezer Tamir wrote: > On 20/05/2013 18:29, Eric Dumazet wrote: > > On Mon, 2013-05-20 at 13:16 +0300, Eliezer Tamir wrote: > --- > >> +static inline void skb_mark_ll(struct sk_buff *skb, struct napi_struct *napi) > >> +{ > >> + skb->dev_ref = napi; > >> +} > >> + > >> +static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb) > >> +{ > >> + sk->dev_ref = skb->dev_ref; > >> +} > > > > I do not see why it's safe to keep a pointer to a napi object without > > taking a reference, or something to prevent object being removed. > > > > Using a genid might be enough. (some counter incremented every time a > > napi is dismantled) > > I really like this approach and I tried it. > The main problem I had is that you need to increase the size of the skb > to store the generation id unless you stuff it in the flags2 bitfield. > There appear to be only 7 useful bit left there. > Is it OK to use them all up? > > > > 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.
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