[xdp-hints] Re: [PATCH bpf-next 05/11] veth: Support rx timestamp metadata for xdp

[Stanislav Fomichev <sdf@google.com>]

On Tue, Nov 15, 2022 at 2:46 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Stanislav Fomichev <sdf@google.com> writes:
>
> > On Tue, Nov 15, 2022 at 8:17 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>
> >> Stanislav Fomichev <sdf@google.com> writes:
> >>
> >> > The goal is to enable end-to-end testing of the metadata
> >> > for AF_XDP. Current rx_timestamp kfunc returns current
> >> > time which should be enough to exercise this new functionality.
> >> >
> >> > Cc: John Fastabend <john.fastabend@gmail.com>
> >> > Cc: David Ahern <dsahern@gmail.com>
> >> > Cc: Martin KaFai Lau <martin.lau@linux.dev>
> >> > Cc: Jakub Kicinski <kuba@kernel.org>
> >> > Cc: Willem de Bruijn <willemb@google.com>
> >> > Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> >> > Cc: Anatoly Burakov <anatoly.burakov@intel.com>
> >> > Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
> >> > Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
> >> > Cc: Maryam Tahhan <mtahhan@redhat.com>
> >> > Cc: xdp-hints@xdp-project.net
> >> > Cc: netdev@vger.kernel.org
> >> > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> >> > ---
> >> >  drivers/net/veth.c | 14 ++++++++++++++
> >> >  1 file changed, 14 insertions(+)
> >> >
> >> > diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> >> > index 2a4592780141..c626580a2294 100644
> >> > --- a/drivers/net/veth.c
> >> > +++ b/drivers/net/veth.c
> >> > @@ -25,6 +25,7 @@
> >> >  #include <linux/filter.h>
> >> >  #include <linux/ptr_ring.h>
> >> >  #include <linux/bpf_trace.h>
> >> > +#include <linux/bpf_patch.h>
> >> >  #include <linux/net_tstamp.h>
> >> >
> >> >  #define DRV_NAME     "veth"
> >> > @@ -1659,6 +1660,18 @@ static int veth_xdp(struct net_device *dev, struct netdev_bpf *xdp)
> >> >       }
> >> >  }
> >> >
> >> > +static void veth_unroll_kfunc(const struct bpf_prog *prog, u32 func_id,
> >> > +                           struct bpf_patch *patch)
> >> > +{
> >> > +     if (func_id == xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP_SUPPORTED)) {
> >> > +             /* return true; */
> >> > +             bpf_patch_append(patch, BPF_MOV64_IMM(BPF_REG_0, 1));
> >> > +     } else if (func_id == xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP)) {
> >> > +             /* return ktime_get_mono_fast_ns(); */
> >> > +             bpf_patch_append(patch, BPF_EMIT_CALL(ktime_get_mono_fast_ns));
> >> > +     }
> >> > +}
> >>
> >> So these look reasonable enough, but would be good to see some examples
> >> of kfunc implementations that don't just BPF_CALL to a kernel function
> >> (with those helper wrappers we were discussing before).
> >
> > Let's maybe add them if/when needed as we add more metadata support?
> > xdp_metadata_export_to_skb has an example, and rfc 1/2 have more
> > examples, so it shouldn't be a problem to resurrect them back at some
> > point?
>
> Well, the reason I asked for them is that I think having to maintain the
> BPF code generation in the drivers is probably the biggest drawback of
> the kfunc approach, so it would be good to be relatively sure that we
> can manage that complexity (via helpers) before we commit to this :)

Right, and I've added a bunch of examples in v2 rfc so we can judge
whether that complexity is manageable or not :-)
Do you want me to add those wrappers you've back without any real users?
Because I had to remove my veth tstamp accessors due to John/Jesper
objections; I can maybe bring some of this back gated by some
static_branch to avoid the fastpath cost?