Re: Deferred if_start

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Mon, Dec 05, 2016 at 12:16:42PM +0900, Ryota Ozaki wrote:
> On Fri, Dec 2, 2016 at 7:55 PM, Joerg Sonnenberger <joerg%bec.de@localhost> wrote:
> > Especially on older systems, adding non-trivial overhead to RX
> > processing can be costly, especially if the technical reasons are
> > questionable. So let's look at those reasons again.
> 
> I think it's trivial because deferred if_start only runs if it's
> requested and the check if it's requested is executed per multiple
> packets, not per packet.

Please remember, I'm not arguing about if_start, but changing RX
processing to include another softint layer.

> BTW, how about moving bpf_mtap (and ifp->if_ipackets++) from each driver
> to the common percpuq if_input? That's also a requirement for MP-safe bpf.

That would work at least for Ethernet drivers. It would actually be nice
to recheck the function pointer at this point, e.g. the way VLAN
processing is hooked up is somewhat gross, but that's unrelated. You
should keep in mind though that some drivers (e.g. WLAN) have multiple
bpf_mtap hooks to include the signal statistics etc.

Joerg