From: Rusty Russell <[EMAIL PROTECTED]>
Date: Tue, 24 Jul 2007 14:47:19 +1000
> On Mon, 2007-07-23 at 21:07 -0700, David Miller wrote:
> > Another area of consternation are drivers that were using
> > netif_rx_reschedule(), as that interface was removed because it
> > doesn't fit well with the caller managing the dev->quota et al. I
> > left race conditions in the drivers that were using that interface,
> > but they should still basically work nonetheless.
>
> Hmm, virtio does this, if the implementation returns false from
> ->restart. But it's basically a bandaid for things like lguest which
> don't check irq status on irq enable, hence is subject to the race.
>
> But AFAICT netif_rx_reschedule() is implementable in a driver anyway.
> What am I missing?
That looks like it would work, yes.
This is the least understood area, semantically, of NAPI. It is
commonly believed that level-triggered interrupts obviate the need to
handle this race condition, and nothing could be further from the
truth.
I don't think it's wise to implement this over and over again in each
driver, since we already know at least a handfull of drivers will use
this.
A netdev_napi_init() suggests itself already. We could put the work
struct into the napi_struct and make the init routine something like:
static inline void netif_napi_init(struct napi_struct *napi,
int (*poll)(struct napi_struct *, int),
void (*resched)(struct work *),
int weight)
{
napi->poll = poll;
napi->weight = weight;
INIT_WORK(&napi->work, resched);
}
and then we have napi_resched():
static inline void napi_resched(struct napi_struct *napi)
{
schedule_work(&napi->work);
}
If this can be handled in a better way inside the driver, as is the
case for tg3 et al., "resched" can be passed in as NULL.
Any objections?
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