> Lorenzo Bianconi wrote:
> > Update multi-buffer bit (mb) in xdp_buff to notify XDP/eBPF layer and
> > XDP remote drivers if this is a "non-linear" XDP buffer. Access
> > skb_shared_info only if xdp_buff mb is set in order to avoid possible
> > cache-misses.
> >
> > Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
>
> [...]
>
> > @@ -2320,8 +2325,12 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct page_pool *pool,
> > struct xdp_buff *xdp, u32 desc_status)
> > {
> > struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> > - int i, num_frags = sinfo->nr_frags;
> > struct sk_buff *skb;
> > + u8 num_frags;
> > + int i;
> > +
> > + if (unlikely(xdp_buff_is_mb(xdp)))
> > + num_frags = sinfo->nr_frags;
>
> Doesn't really need a respin IMO, but rather an observation. Its not
> obvious to me the unlikely/likely pair here is wanted. Seems it could
> be relatively common for some applications sending jumbo frames.
>
> Maybe worth some experimenting in the future.
Probably for mvneta it will not make any difference but in general I tried to
avoid possible cache-misses here (accessing sinfo pointers). I will carry out
some comparison to see if I can simplify the code.
Regards,
Lorenzo
>
> >
> > skb = build_skb(xdp->data_hard_start, PAGE_SIZE);
> > if (!skb)
> > @@ -2333,6 +2342,9 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct page_pool *pool,
> > skb_put(skb, xdp->data_end - xdp->data);
> > skb->ip_summed = mvneta_rx_csum(pp, desc_status);
> >
> > + if (likely(!xdp_buff_is_mb(xdp)))
> > + goto out;
> > +
> > for (i = 0; i < num_frags; i++) {
> > skb_frag_t *frag = &sinfo->frags[i];
>
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