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

Jarek Poplawski
2010-08-28T14:31:38Z

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?

Jarek P.