netdev - Re: [RFC] gro: Is it ok to share a single napi from several devs ?

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Message-ID: <20100828143132.GA3211@del.dom.local>
Date:	Sat, 28 Aug 2010 16:31:32 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC] gro: Is it ok to share a single napi from several devs ?

On Sat, Aug 28, 2010 at 12:54:06PM +0200, Eric Dumazet wrote:
> In commit f2bde7328633269ee935d9ed96535ade15cc348f
> Author: Stephen Hemminger <shemminger@...tta.com>
> 
>     net: allow multiple dev per napi with GRO
>     
>     GRO assumes that there is a one-to-one relationship between NAPI
>     structure and network device. Some devices like sky2 share multiple
>     devices on a single interrupt so only have one NAPI handler. Rather than
>     split GRO from NAPI, just have GRO assume if device changes that
>     it is a different flow.
>    
> 
> It was assumed a napi could be shared by several devs, but I dont really
> understand, since we have an unique ->dev pointer inside "napi_struct",
> this one is set once, and never change.
> 
> This pointer is currently used from napi_get_frags() [but that could be
> avoided], and from netpoll_poll_lock().
> 
> The netpoll_poll_lock() case is problematic.
> 
> static inline void *netpoll_poll_lock(struct napi_struct *napi)
> {
>         struct net_device *dev = napi->_dev;
> 
>         if (dev && dev->npinfo) {
>                 spin_lock(&napi->poll_lock);
> 
> Maybe we should remove 'dev' field from napi_struct and replace it by a
> npinfo pointer ?

Sky2 seems to work like a single netdev (with an internal sub-netdev),
so I can't see your concern: what is the main aim of this replacement?

Jarek P. 
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