net: ipv6: rpl_iptunnel: mitigate 2-realloc issue

This patch mitigates the two-reallocations issue with rpl_iptunnel by
providing the dst_entry (in the cache) to the first call to
skb_cow_head(). As a result, the very first iteration would still
trigger two reallocations (i.e., empty cache), while next iterations
would only trigger a single reallocation.

Performance tests before/after applying this patch, which clearly shows
there is no impact (it even shows improvement):
- before: https://ibb.co/nQJhqwc
- after: https://ibb.co/4ZvW6wV

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Cc: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c
index db3c19a42e1ca71bada33d0f776ccc42572c9f81..7ba22d2f2bfefa73a9fcaed0fab50d8a5afc1cad 100644 (file)
--- a/net/ipv6/rpl_iptunnel.c
+++ b/net/ipv6/rpl_iptunnel.c
@@ -125,7 +125,8 @@ static void rpl_destroy_state(struct lwtunnel_state *lwt)
 }
 
 static int rpl_do_srh_inline(struct sk_buff *skb, const struct rpl_lwt *rlwt,
-                            const struct ipv6_rpl_sr_hdr *srh)
+                            const struct ipv6_rpl_sr_hdr *srh,
+                            struct dst_entry *cache_dst)
 {
        struct ipv6_rpl_sr_hdr *isrh, *csrh;
        const struct ipv6hdr *oldhdr;
@@ -153,7 +154,7 @@ static int rpl_do_srh_inline(struct sk_buff *skb, const struct rpl_lwt *rlwt,
 
        hdrlen = ((csrh->hdrlen + 1) << 3);
 
-       err = skb_cow_head(skb, hdrlen + skb->mac_len);
+       err = skb_cow_head(skb, hdrlen + dst_dev_overhead(cache_dst, skb));
        if (unlikely(err)) {
                kfree(buf);
                return err;
@@ -186,7 +187,8 @@ static int rpl_do_srh_inline(struct sk_buff *skb, const struct rpl_lwt *rlwt,
        return 0;
 }
 
-static int rpl_do_srh(struct sk_buff *skb, const struct rpl_lwt *rlwt)
+static int rpl_do_srh(struct sk_buff *skb, const struct rpl_lwt *rlwt,
+                     struct dst_entry *cache_dst)
 {
        struct dst_entry *dst = skb_dst(skb);
        struct rpl_iptunnel_encap *tinfo;
@@ -196,7 +198,7 @@ static int rpl_do_srh(struct sk_buff *skb, const struct rpl_lwt *rlwt)
 
        tinfo = rpl_encap_lwtunnel(dst->lwtstate);
 
-       return rpl_do_srh_inline(skb, rlwt, tinfo->srh);
+       return rpl_do_srh_inline(skb, rlwt, tinfo->srh, cache_dst);
 }
 
 static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
@@ -208,14 +210,14 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 
        rlwt = rpl_lwt_lwtunnel(orig_dst->lwtstate);
 
-       err = rpl_do_srh(skb, rlwt);
-       if (unlikely(err))
-               goto drop;
-
        local_bh_disable();
        dst = dst_cache_get(&rlwt->cache);
        local_bh_enable();
 
+       err = rpl_do_srh(skb, rlwt, dst);
+       if (unlikely(err))
+               goto drop;
+
        if (unlikely(!dst)) {
                struct ipv6hdr *hdr = ipv6_hdr(skb);
                struct flowi6 fl6;
@@ -237,15 +239,15 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
                local_bh_disable();
                dst_cache_set_ip6(&rlwt->cache, dst, &fl6.saddr);
                local_bh_enable();
+
+               err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
+               if (unlikely(err))
+                       goto drop;
        }
 
        skb_dst_drop(skb);
        skb_dst_set(skb, dst);
 
-       err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
-       if (unlikely(err))
-               goto drop;
-
        return dst_output(net, sk, skb);
 
 drop:
@@ -262,29 +264,31 @@ static int rpl_input(struct sk_buff *skb)
 
        rlwt = rpl_lwt_lwtunnel(orig_dst->lwtstate);
 
-       err = rpl_do_srh(skb, rlwt);
-       if (unlikely(err))
-               goto drop;
-
        local_bh_disable();
        dst = dst_cache_get(&rlwt->cache);
+       local_bh_enable();
+
+       err = rpl_do_srh(skb, rlwt, dst);
+       if (unlikely(err))
+               goto drop;
 
        if (!dst) {
                ip6_route_input(skb);
                dst = skb_dst(skb);
                if (!dst->error) {
+                       local_bh_disable();
                        dst_cache_set_ip6(&rlwt->cache, dst,
                                          &ipv6_hdr(skb)->saddr);
+                       local_bh_enable();
                }
+
+               err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
+               if (unlikely(err))
+                       goto drop;
        } else {
                skb_dst_drop(skb);
                skb_dst_set(skb, dst);
        }
-       local_bh_enable();
-
-       err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
-       if (unlikely(err))
-               goto drop;
 
        return dst_input(skb);