[RFC PATCH net-next v2 2/3] net: dst_cache: add input_dst_cache API

[Leone Fernando]

The input_dst_cache allows fast lookup of frequently encountered dsts.

In order to provide stable results, I implemented a simple linear
hashtable with each bucket containing a constant amount of
entries (DST_CACHE_INPUT_BUCKET_SIZE).

Similarly to how the route hint is used, I defined the hashtable key to
contain the daddr and the tos of the IP header.

Lookup is performed in a straightforward manner: start at the bucket head
corresponding the hashed key and search the following
DST_CACHE_INPUT_BUCKET_SIZE entries of the array for a matching key.

When inserting a new dst to the cache, if all the bucket entries are
full, the oldest one is deleted to make room for the new dst.

Signed-off-by: Leone Fernando <leone4fernando@xxxxxxxxx>
---
 include/net/dst_cache.h |  69 +++++++++++++++++++++
 net/core/dst_cache.c    | 132 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 201 insertions(+)

diff --git a/include/net/dst_cache.h b/include/net/dst_cache.h
index df6622a5fe98..4c5474c44cad 100644
--- a/include/net/dst_cache.h
+++ b/include/net/dst_cache.h
@@ -7,12 +7,40 @@
 #if IS_ENABLED(CONFIG_IPV6)
 #include <net/ip6_fib.h>
 #endif
+#include <net/ip.h>
+
+#define DST_CACHE_INPUT_SHIFT (9)
+#define DST_CACHE_INPUT_SIZE (1 << DST_CACHE_INPUT_SHIFT)
+#define DST_CACHE_INPUT_BUCKET_SIZE (4)
+#define DST_CACHE_INPUT_HASH_MASK (~(DST_CACHE_INPUT_BUCKET_SIZE - 1))
+#define INVALID_DST_CACHE_INPUT_KEY (~(u64)(0))
 
 struct dst_cache {
 	struct dst_cache_pcpu __percpu *cache;
 	unsigned long reset_ts;
 };
 
+extern unsigned int dst_cache_net_id __read_mostly;
+
+/**
+ * idst_for_each_in_bucket - iterate over a dst cache bucket
+ * @pos:	the type * to use as a loop cursor
+ * @head:	the head of the cpu dst cache.
+ * @hash:	the hash of the bucket
+ */
+#define idst_for_each_in_bucket(pos, head, hash)		\
+	for (pos = &head[hash];					\
+	     pos < &head[hash + DST_CACHE_INPUT_BUCKET_SIZE];	\
+	     pos++)
+
+/**
+ * idst_for_each_in_cache - iterate over the dst cache
+ * @pos:	the type * to use as a loop cursor
+ * @head:	the head of the cpu dst cache.
+ */
+#define idst_for_each_in_cache(pos, head)				\
+	for (pos = head; pos < head + DST_CACHE_INPUT_SIZE; pos++)
+
 /**
  *	dst_cache_get - perform cache lookup
  *	@dst_cache: the cache
@@ -106,4 +134,45 @@ int dst_cache_init(struct dst_cache *dst_cache, gfp_t gfp);
  */
 void dst_cache_destroy(struct dst_cache *dst_cache);
 
+/**
+ *	dst_cache_input_get_noref - perform lookup in the input cache,
+ *	return a noref dst
+ *	@dst_cache: the input cache
+ *	@skb: the packet according to which the dst entry will be searched
+ *	local BH must be disabled.
+ */
+struct dst_entry *dst_cache_input_get_noref(struct dst_cache *dst_cache,
+					    struct sk_buff *skb);
+
+/**
+ *	dst_cache_input_add - add the dst of the given skb to the input cache.
+ *
+ *	in case the cache bucket is full, the oldest entry will be deleted
+ *	and replaced with the new one.
+ *	@dst_cache: the input cache
+ *	@skb: The packet according to which the dst entry will be searched
+ *
+ *	local BH must be disabled.
+ */
+void dst_cache_input_add(struct dst_cache *dst_cache,
+			 const struct sk_buff *skb);
+
+/**
+ *	dst_cache_input_init - initialize the input cache,
+ *	allocating the required storage
+ */
+int __init dst_cache_input_init(void);
+
+static inline u64 create_dst_cache_key_ip4(const struct sk_buff *skb)
+{
+	struct iphdr *iphdr = ip_hdr(skb);
+
+	return (((u64)iphdr->daddr) << 8) | iphdr->tos;
+}
+
+static inline u32 hash_dst_cache_key(u64 key)
+{
+	return hash_64(key, DST_CACHE_INPUT_SHIFT) & DST_CACHE_INPUT_HASH_MASK;
+}
+
 #endif
diff --git a/net/core/dst_cache.c b/net/core/dst_cache.c
index 0ccfd5fa5cb9..e551b9ce5108 100644
--- a/net/core/dst_cache.c
+++ b/net/core/dst_cache.c
@@ -13,6 +13,7 @@
 #include <net/ip6_fib.h>
 #endif
 #include <uapi/linux/in.h>
+#include <net/netns/generic.h>
 
 struct dst_cache_pcpu {
 	unsigned long refresh_ts;
@@ -21,9 +22,12 @@ struct dst_cache_pcpu {
 	union {
 		struct in_addr in_saddr;
 		struct in6_addr in6_saddr;
+		u64 key;
 	};
 };
 
+unsigned int dst_cache_net_id __read_mostly;
+
 static void dst_cache_per_cpu_dst_set(struct dst_cache_pcpu *dst_cache,
 				      struct dst_entry *dst, u32 cookie)
 {
@@ -181,3 +185,131 @@ void dst_cache_reset_now(struct dst_cache *dst_cache)
 	}
 }
 EXPORT_SYMBOL_GPL(dst_cache_reset_now);
+
+static void dst_cache_input_set(struct dst_cache_pcpu *idst,
+				struct dst_entry *dst, u64 key)
+{
+	dst_cache_per_cpu_dst_set(idst, dst, 0);
+	idst->key = key;
+	idst->refresh_ts = jiffies;
+}
+
+static struct dst_entry *__dst_cache_input_get_noref(struct dst_cache_pcpu *idst)
+{
+	struct dst_entry *dst = idst->dst;
+
+	if (unlikely(dst->obsolete && !dst->ops->check(dst, idst->cookie))) {
+		dst_cache_input_set(idst, NULL, INVALID_DST_CACHE_INPUT_KEY);
+		goto fail;
+	}
+
+	idst->refresh_ts = jiffies;
+	return dst;
+
+fail:
+	return NULL;
+}
+
+struct dst_entry *dst_cache_input_get_noref(struct dst_cache *dst_cache,
+					    struct sk_buff *skb)
+{
+	struct dst_entry *out_dst = NULL;
+	struct dst_cache_pcpu *pcpu_cache;
+	struct dst_cache_pcpu *idst;
+	u32 hash;
+	u64 key;
+
+	pcpu_cache = this_cpu_ptr(dst_cache->cache);
+	key = create_dst_cache_key_ip4(skb);
+	hash = hash_dst_cache_key(key);
+	idst_for_each_in_bucket(idst, pcpu_cache, hash) {
+		if (key == idst->key) {
+			out_dst = __dst_cache_input_get_noref(idst);
+			goto out;
+		}
+	}
+out:
+	return out_dst;
+}
+
+static void dst_cache_input_reset_now(struct dst_cache *dst_cache)
+{
+	struct dst_cache_pcpu *caches;
+	struct dst_cache_pcpu *idst;
+	struct dst_entry *dst;
+	int i;
+
+	for_each_possible_cpu(i) {
+		caches = per_cpu_ptr(dst_cache->cache, i);
+		idst_for_each_in_cache(idst, caches) {
+			idst->key = INVALID_DST_CACHE_INPUT_KEY;
+			dst = idst->dst;
+			if (dst)
+				dst_release(dst);
+		}
+	}
+}
+
+static int __net_init dst_cache_input_net_init(struct net *net)
+{
+	struct dst_cache *dst_cache = net_generic(net, dst_cache_net_id);
+
+	dst_cache->cache = (struct dst_cache_pcpu __percpu *)alloc_percpu_gfp(struct dst_cache_pcpu[DST_CACHE_INPUT_SHIFT],
+									      GFP_KERNEL | __GFP_ZERO);
+	if (!dst_cache->cache)
+		return -ENOMEM;
+
+	dst_cache_input_reset_now(dst_cache);
+	return 0;
+}
+
+static void __net_exit dst_cache_input_net_exit(struct net *net)
+{
+	struct dst_cache *dst_cache = net_generic(net, dst_cache_net_id);
+
+	dst_cache_input_reset_now(dst_cache);
+	free_percpu(dst_cache->cache);
+	dst_cache->cache = NULL;
+}
+
+static bool idst_empty(struct dst_cache_pcpu *idst)
+{
+	return idst->key == INVALID_DST_CACHE_INPUT_KEY;
+}
+
+void dst_cache_input_add(struct dst_cache *dst_cache, const struct sk_buff *skb)
+{
+	struct dst_cache_pcpu *entry = NULL;
+	struct dst_cache_pcpu *pcpu_cache;
+	struct dst_cache_pcpu *idst;
+	u32 hash;
+	u64 key;
+
+	pcpu_cache = this_cpu_ptr(dst_cache->cache);
+	key = create_dst_cache_key_ip4(skb);
+	hash = hash_dst_cache_key(key);
+	idst_for_each_in_bucket(idst, pcpu_cache, hash) {
+		if (idst_empty(idst)) {
+			entry = idst;
+			goto add_to_cache;
+		}
+		if (!entry || time_before(idst->refresh_ts, entry->refresh_ts))
+			entry = idst;
+	}
+
+add_to_cache:
+	dst_cache_input_set(entry, skb_dst(skb), key);
+}
+
+static struct pernet_operations dst_cache_input_ops __net_initdata = {
+	.init = dst_cache_input_net_init,
+	.exit = dst_cache_input_net_exit,
+	.id   = &dst_cache_net_id,
+	.size = sizeof(struct dst_cache),
+};
+
+int __init dst_cache_input_init(void)
+{
+	return register_pernet_subsys(&dst_cache_input_ops);
+}
+subsys_initcall(dst_cache_input_init);
-- 
2.34.1