RE: [PATCH v19 bpf-next 03/23] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer
From: John Fastabend <john.fastabend@gmail.com>
Date: 2021-12-06 03:07:07
Also in:
bpf
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@kernel.org>
[...]
quoted hunk ↗ jump to hunk
@@ -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.
quoted hunk ↗ jump to hunk
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];