Re: [RFC PATCH v2 02/10] udp: implement GRO for plain UDP sockets.
From: Steffen Klassert <steffen.klassert@secunet.com>
Date: 2018-10-22 19:43:02
On Fri, Oct 19, 2018 at 04:25:12PM +0200, Paolo Abeni wrote:
+#define UDO_GRO_CNT_MAX 64
Maybe better UDP_GRO_CNT_MAX? Btw. do we really need this explicit limit? We should not get more than 64 packets during one napi poll cycle.
+static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
+ struct sk_buff *skb)
+{
+ struct udphdr *uh = udp_hdr(skb);
+ struct sk_buff *pp = NULL;
+ struct udphdr *uh2;
+ struct sk_buff *p;
+
+ /* requires non zero csum, for simmetry with GSO */
+ if (!uh->check) {
+ NAPI_GRO_CB(skb)->flush = 1;
+ return NULL;
+ }Why is the requirement of checksums different than in udp_gro_receive? It's not that I care much about UDP packets without a checksum, but you would not need to implement your own loop if the requirement could be the same as in udp_gro_receive.
+
+ /* pull encapsulating udp header */
+ skb_gro_pull(skb, sizeof(struct udphdr));
+ skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
+
+ list_for_each_entry(p, head, list) {
+ if (!NAPI_GRO_CB(p)->same_flow)
+ continue;
+
+ uh2 = udp_hdr(p);
+
+ /* Match ports only, as csum is always non zero */
+ if ((*(u32 *)&uh->source != *(u32 *)&uh2->source)) {
+ NAPI_GRO_CB(p)->same_flow = 0;
+ continue;
+ }
+
+ /* Terminate the flow on len mismatch or if it grow "too much".
+ * Under small packet flood GRO count could elsewhere grow a lot
+ * leading to execessive truesize values
+ */
+ if (!skb_gro_receive(p, skb) &&
+ NAPI_GRO_CB(p)->count > UDO_GRO_CNT_MAX)This allows to merge UDO_GRO_CNT_MAX + 1 packets.
+ pp = p; + else if (uh->len != uh2->len) + pp = p; + + return pp; + } + + /* mismatch, but we never need to flush */ + return NULL; +}