On Tue, 8 Oct 2019 at 08:59, Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> Sridhar Samudrala <sridhar.samudrala@xxxxxxxxx> writes:
>
> > int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
> > struct bpf_prog *xdp_prog)
> > {
> > struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> > struct bpf_map *map = READ_ONCE(ri->map);
> > + struct xdp_sock *xsk;
> > +
> > + xsk = xdp_get_direct_xsk(ri);
> > + if (xsk)
> > + return xsk_rcv(xsk, xdp);
>
> This is a new branch and a read barrier in the XDP_REDIRECT fast path.
> What's the performance impact of that for non-XSK redirect?
>
The dependent-read-barrier in READ_ONCE? Another branch -- leave that
to the branch-predictor already! ;-) No, you're right, performance
impact here is interesting. I guess the same static_branch could be
used here as well...
> -Toke
>
