[net-next PATCH] bpf: cpumap micro-optimization in cpu_map_enqueue
From: Jesper Dangaard Brouer <hidden>
Date: 2017-11-01 11:44:49
Subsystem:
bpf [general] (safe dynamic programs and tools), the rest, xdp (express data path) · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds, David S. Miller, Jakub Kicinski, Jesper Dangaard Brouer, John Fastabend
Discovered that the compiler laid-out asm code in suboptimal way when studying perf report during benchmarking of cpumap. Help the compiler by the marking unlikely code paths. Signed-off-by: Jesper Dangaard Brouer <redacted> --- kernel/bpf/cpumap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 86e29cbf7827..ce5b669003b2 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c@@ -208,7 +208,7 @@ static struct xdp_pkt *convert_to_xdp_pkt(struct xdp_buff *xdp) headroom = xdp->data - xdp->data_hard_start; metasize = xdp->data - xdp->data_meta; metasize = metasize > 0 ? metasize : 0; - if ((headroom - metasize) < sizeof(*xdp_pkt)) + if (unlikely((headroom - metasize) < sizeof(*xdp_pkt))) return NULL; /* Store info in top of packet */
@@ -656,7 +656,7 @@ int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp, struct xdp_pkt *xdp_pkt; xdp_pkt = convert_to_xdp_pkt(xdp); - if (!xdp_pkt) + if (unlikely(!xdp_pkt)) return -EOVERFLOW; /* Info needed when constructing SKB on remote CPU */