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authorJesper Dangaard Brouer <brouer@redhat.com>2020-05-14 12:49:38 +0200
committerAlexei Starovoitov <ast@kernel.org>2020-05-14 21:21:54 -0700
commitdb612f749e2454c506f20155bba2871f0307d133 (patch)
tree6c06de2552a875163ec1c586cc03cd2c104c0c67 /kernel
parent34cc0b338a61de3eee3a2bfcaf4f9d6e9fae091a (diff)
xdp: Cpumap redirect use frame_sz and increase skb_tailroom
Knowing the memory size backing the packet/xdp_frame data area, and knowing it already have reserved room for skb_shared_info, simplifies using build_skb significantly. With this change we no-longer lie about the SKB truesize, but more importantly a significant larger skb_tailroom is now provided, e.g. when drivers uses a full PAGE_SIZE. This extra tailroom (in linear area) can be used by the network stack when coalescing SKBs (e.g. in skb_try_coalesce, see TCP cases where tcp_queue_rcv() can 'eat' skb). Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> Link: https://lore.kernel.org/bpf/158945337822.97035.13557959180460986059.stgit@firesoul
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/cpumap.c21
1 files changed, 3 insertions, 18 deletions
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 3fe0b006d2d2..a71790dab12d 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -162,25 +162,10 @@ static struct sk_buff *cpu_map_build_skb(struct bpf_cpu_map_entry *rcpu,
/* Part of headroom was reserved to xdpf */
hard_start_headroom = sizeof(struct xdp_frame) + xdpf->headroom;
- /* build_skb need to place skb_shared_info after SKB end, and
- * also want to know the memory "truesize". Thus, need to
- * know the memory frame size backing xdp_buff.
- *
- * XDP was designed to have PAGE_SIZE frames, but this
- * assumption is not longer true with ixgbe and i40e. It
- * would be preferred to set frame_size to 2048 or 4096
- * depending on the driver.
- * frame_size = 2048;
- * frame_len = frame_size - sizeof(*xdp_frame);
- *
- * Instead, with info avail, skb_shared_info in placed after
- * packet len. This, unfortunately fakes the truesize.
- * Another disadvantage of this approach, the skb_shared_info
- * is not at a fixed memory location, with mixed length
- * packets, which is bad for cache-line hotness.
+ /* Memory size backing xdp_frame data already have reserved
+ * room for build_skb to place skb_shared_info in tailroom.
*/
- frame_size = SKB_DATA_ALIGN(xdpf->len + hard_start_headroom) +
- SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ frame_size = xdpf->frame_sz;
pkt_data_start = xdpf->data - hard_start_headroom;
skb = build_skb_around(skb, pkt_data_start, frame_size);