>
> On 02/07/2025 16.58, Jesper Dangaard Brouer wrote:
> > From: Lorenzo Bianconi<lorenzo@xxxxxxxxxx>
> >
> > Introduce the following kfuncs to store hw metadata provided by the NIC
> > into the xdp_buff struct:
> >
> > - rx-hash: bpf_xdp_store_rx_hash
> > - rx-vlan: bpf_xdp_store_rx_vlan
> > - rx-hw-ts: bpf_xdp_store_rx_ts
> >
> > Signed-off-by: Lorenzo Bianconi<lorenzo@xxxxxxxxxx>
> > Signed-off-by: Jesper Dangaard Brouer<hawk@xxxxxxxxxx>
> > ---
> > include/net/xdp.h | 5 +++++
> > net/core/xdp.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 50 insertions(+)
> >
> > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > index bd3110fc7ef8..1ffba57714ea 100644
> > --- a/net/core/xdp.c
> > +++ b/net/core/xdp.c
> > @@ -963,12 +963,57 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx,
> [...]
> > +__bpf_kfunc int bpf_xdp_store_rx_ts(struct xdp_md *ctx, u64 ts)
> > +{
> > + struct xdp_buff *xdp = (struct xdp_buff *)ctx;
> > + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> > + struct skb_shared_hwtstamps *shwt = &sinfo->hwtstamps;
> > +
> > + shwt->hwtstamp = ts;
>
> Here we are storing into the SKB shared_info struct. This is located at
> the SKB data tail. Thus, this will very likely cause a cache-miss.
>
> What about storing it into xdp->rx_meta and then starting a prefetch for
> shared_info? (and updating patch-4 that moved it into SKB)
ack, I am fine with it. I can address it in v3.
Regards,
Lorenzo
>
> (Reviewers should be aware that writing into the xdp_frame headroom
> (xdp->rx_meta) likely isn't a cache-miss, because all drivers does a
> prefetchw for this memory prior to running BPF-prog).
>
>
> > + xdp->flags |= XDP_FLAGS_META_RX_TS;
> > +
> > + return 0;
> > +}
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