Re: [PATCH bpf-next v2 0/8] Simplify xdp_do_redirect_map()/xdp_do_flush_map() and XDP maps

Jesper Dangaard Brouer
2020-01-07T13:06:04Z

On Tue, 07 Jan 2020 12:25:47 +0100
Toke Høiland-Jørgensen <toke@redhat.com> wrote:

> Björn Töpel <bjorn.topel@gmail.com> writes:
>
> > On Fri, 20 Dec 2019 at 11:30, Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>
> >> Jesper Dangaard Brouer <brouer@redhat.com> writes:
> >>
> > [...]
> >> > I have now went over the entire patchset, and everything look perfect,
> >> > I will go as far as saying it is brilliant. We previously had the
> >> > issue, that using different redirect maps in a BPF-prog would cause the
> >> > bulking effect to be reduced, as map_to_flush cause previous map to get
> >> > flushed. This is now solved :-)
> >>
> >> Another thing that occurred to me while thinking about this: Now that we
> >> have a single flush list, is there any reason we couldn't move the
> >> devmap xdp_bulk_queue into struct net_device? That way it could also be
> >> used for the non-map variant of bpf_redirect()?
> >>
> >
> > Indeed! (At least I don't see any blockers...)
>
> Cool, that's what I thought. Maybe I'll give that a shot, then, unless
> you beat me to it ;)

Generally sounds like a good idea.

It this only for devmap xdp_bulk_queue?

Some gotchas off the top of my head.

The cpumap also have a struct xdp_bulk_queue, which have a different
layout. (sidenote: due to BTF we likely want rename that).

If you want to generalize this across all redirect maps type. You
should know, that it was on purpose that I designed the bulking to be
map specific, because that allowed each map to control its own optimal
bulking. E.g. devmap does 16 frames bulking, cpumap does 8 frames (as
it matches sending 1 cacheline into underlying ptr_ring), xskmap does
64 AFAIK (which could hurt-latency, but that is another discussion).

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer