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

Eric Dumazet
2010-08-28T14:48:35Z

Le samedi 28 août 2010 à 16:31 +0200, Jarek Poplawski a écrit :
> On Sat, Aug 28, 2010 at 12:54:06PM +0200, Eric Dumazet wrote:
> > In commit f2bde7328633269ee935d9ed96535ade15cc348f
> > Author: Stephen Hemminger <shemminger@vyatta.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?

I am trying to understand why this commit was needed then.

It adds an extra test in the main loop, testing skb->dev against p->dev,
it must me for something...

I am trying to say that the one to one relationship between NAPI
structure and a device is not only a GRO thing, but also a netpoll one.

So either we completely remove this one to one relationship, either
Stephen commit was not needed.

Some clarification is needed.