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

[Eliezer Tamir <eliezer.tamir@linux.intel.com>]

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.

-Eliezer