On Wed, Sep 1, 2021 at 1:24 AM John Fastabend <john.fastabend@xxxxxxxxx> wrote:
>
> 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>
> > ---
> > drivers/net/ethernet/marvell/mvneta.c | 23 ++++++++++++++++++-----
> > 1 file changed, 18 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > index 5d1007e1b5c9..9f4858e35566 100644
> > --- a/drivers/net/ethernet/marvell/mvneta.c
> > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > @@ -2037,9 +2037,14 @@ mvneta_xdp_put_buff(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
> > {
> > int i;
> >
> > + if (likely(!xdp_buff_is_mb(xdp)))
> > + goto out;
> > +
>
> Wouldn't nr_frags = 0 in the !xdp_buff_is_mb case? Is the
> xdp_buff_is_mb check with goto really required?
if xdp_buff_is_mb is false, nr_frags will not be initialized otherwise
we will trigger a cache-miss for the single-buffer use case (where
initializing skb_shared_info is not required).
>
> > for (i = 0; i < sinfo->nr_frags; i++)
> > page_pool_put_full_page(rxq->page_pool,
> > skb_frag_page(&sinfo->frags[i]), true);
> > +
> > +out:
> > page_pool_put_page(rxq->page_pool, virt_to_head_page(xdp->data),
> > sync_len, true);
> > }
> > @@ -2241,7 +2246,6 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
> > int data_len = -MVNETA_MH_SIZE, len;
> > struct net_device *dev = pp->dev;
> > enum dma_data_direction dma_dir;
> > - struct skb_shared_info *sinfo;
> >
> > if (*size > MVNETA_MAX_RX_BUF_SIZE) {
> > len = MVNETA_MAX_RX_BUF_SIZE;
> > @@ -2261,11 +2265,9 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
> >
> > /* Prefetch header */
> > prefetch(data);
> > + xdp_buff_clear_mb(xdp);
> > xdp_prepare_buff(xdp, data, pp->rx_offset_correction + MVNETA_MH_SIZE,
> > data_len, false);
> > -
> > - sinfo = xdp_get_shared_info_from_buff(xdp);
> > - sinfo->nr_frags = 0;
> > }
> >
> > static void
> > @@ -2299,6 +2301,9 @@ mvneta_swbm_add_rx_fragment(struct mvneta_port *pp,
> > skb_frag_off_set(frag, pp->rx_offset_correction);
> > skb_frag_size_set(frag, data_len);
> > __skb_frag_set_page(frag, page);
> > +
> > + if (!xdp_buff_is_mb(xdp))
> > + xdp_buff_set_mb(xdp);
> > } else {
> > page_pool_put_full_page(rxq->page_pool, page, true);
> > }
> > @@ -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;
> >
> > 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;
> > +
>
> Not that I care much, but couldn't you just init num_frags = 0 and
> avoid the goto?
same here.
Regards,
Lorenzo
>
> Anyways its not my driver so no need to change it if you like it better
> the way it is. Mostly just checking my understanding.
>
> > for (i = 0; i < num_frags; i++) {
> > skb_frag_t *frag = &sinfo->frags[i];
> >
> > @@ -2341,6 +2353,7 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct page_pool *pool,
> > skb_frag_size(frag), PAGE_SIZE);
> > }
> >
> > +out:
> > return skb;
> > }
> >
> > --
> > 2.31.1
> >
>
>
