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 10:28:55 +0300
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	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 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
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