net: core: rework basic flow dissection helper

When the core networking needs to detect the transport offset in a given
packet and parse it explicitly, a full-blown flow_keys struct is used for
storage.
This patch introduces a smaller keys store, rework the basic flow dissect
helper to use it, and apply this new helper where possible - namely in
skb_probe_transport_header(). The used flow dissector data structures
are renamed to match more closely the new role.

The above gives ~50% performance improvement in micro benchmarking around
skb_probe_transport_header() and ~30% around eth_get_headlen(), mostly due
to the smaller memset. Small, but measurable improvement is measured also
in macro benchmarking.

v1 -> v2: use the new helper in eth_get_headlen() and skb_get_poff(),
  as per DaveM suggestion

Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 12 insertions, 11 deletions

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d29f09bc5ff9..030d4ca177fb 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1253,7 +1253,7 @@ __u32 skb_get_hash_perturb(const struct sk_buff *skb, u32 perturb)
 EXPORT_SYMBOL(skb_get_hash_perturb);
 
 u32 __skb_get_poff(const struct sk_buff *skb, void *data,
-		   const struct flow_keys *keys, int hlen)
+		   const struct flow_keys_basic *keys, int hlen)
 {
 	u32 poff = keys->control.thoff;
 
@@ -1314,9 +1314,9 @@ u32 __skb_get_poff(const struct sk_buff *skb, void *data,
  */
 u32 skb_get_poff(const struct sk_buff *skb)
 {
-	struct flow_keys keys;
+	struct flow_keys_basic keys;
 
-	if (!skb_flow_dissect_flow_keys(skb, &keys, 0))
+	if (!skb_flow_dissect_flow_keys_basic(skb, &keys, 0, 0, 0, 0, 0))
 		return 0;
 
 	return __skb_get_poff(skb, skb->data, &keys, skb_headlen(skb));
@@ -1403,7 +1403,7 @@ static const struct flow_dissector_key flow_keys_dissector_symmetric_keys[] = {
 	},
 };
 
-static const struct flow_dissector_key flow_keys_buf_dissector_keys[] = {
+static const struct flow_dissector_key flow_keys_basic_dissector_keys[] = {
 	{
 		.key_id = FLOW_DISSECTOR_KEY_CONTROL,
 		.offset = offsetof(struct flow_keys, control),
@@ -1417,7 +1417,8 @@ static const struct flow_dissector_key flow_keys_buf_dissector_keys[] = {
 struct flow_dissector flow_keys_dissector __read_mostly;
 EXPORT_SYMBOL(flow_keys_dissector);
 
-struct flow_dissector flow_keys_buf_dissector __read_mostly;
+struct flow_dissector flow_keys_basic_dissector __read_mostly;
+EXPORT_SYMBOL(flow_keys_basic_dissector);
 
 static int __init init_default_flow_dissectors(void)
 {
@@ -1427,9 +1428,9 @@ static int __init init_default_flow_dissectors(void)
 	skb_flow_dissector_init(&flow_keys_dissector_symmetric,
 				flow_keys_dissector_symmetric_keys,
 				ARRAY_SIZE(flow_keys_dissector_symmetric_keys));
-	skb_flow_dissector_init(&flow_keys_buf_dissector,
-				flow_keys_buf_dissector_keys,
-				ARRAY_SIZE(flow_keys_buf_dissector_keys));
+	skb_flow_dissector_init(&flow_keys_basic_dissector,
+				flow_keys_basic_dissector_keys,
+				ARRAY_SIZE(flow_keys_basic_dissector_keys));
 	return 0;
 }
 
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index eaeba9b99a73..ee28440f57c5 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -128,15 +128,15 @@ u32 eth_get_headlen(void *data, unsigned int len)
 {
 	const unsigned int flags = FLOW_DISSECTOR_F_PARSE_1ST_FRAG;
 	const struct ethhdr *eth = (const struct ethhdr *)data;
-	struct flow_keys keys;
+	struct flow_keys_basic keys;
 
 	/* this should never happen, but better safe than sorry */
 	if (unlikely(len < sizeof(*eth)))
 		return len;
 
 	/* parse any remaining L2/L3 headers, check for L4 */
-	if (!skb_flow_dissect_flow_keys_buf(&keys, data, eth->h_proto,
-					    sizeof(*eth), len, flags))
+	if (!skb_flow_dissect_flow_keys_basic(NULL, &keys, data, eth->h_proto,
+					      sizeof(*eth), len, flags))
 		return max_t(u32, keys.control.thoff, sizeof(*eth));
 
 	/* parse for any L4 headers */