netdev - [PATCH net-next] net: core: rework skb_probe_transport

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Date:   Thu,  3 May 2018 11:35:35 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jason Wang <jasowang@...hat.com>
Subject: [PATCH net-next] net: core: rework skb_probe_transport_header()

When the transport header is not available, skb_probe_transport_header()
resorts to fully dissect the flow keys, even if it only needs the
ransport offset. We can obtain the latter using a simpler flow dissector -
flow_keys_buf_dissector - and a smaller struct for key storage.

The above gives ~50% performance improvement in micro benchmarking around
skb_probe_transport_header(), mostly due to the smaller memset. Small, but
measurable improvement is measured also in macro benchmarking - raw xmit
tput from a VM.

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 include/linux/skbuff.h       | 7 +++++--
 include/net/flow_dissector.h | 5 +++++
 net/core/flow_dissector.c    | 1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 908d66e55b14..63cb523d3519 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2350,11 +2350,14 @@ static inline void skb_pop_mac_header(struct sk_buff *skb)
 static inline void skb_probe_transport_header(struct sk_buff *skb,
 					      const int offset_hint)
 {
-	struct flow_keys keys;
+	struct flow_keys_basic keys;
 
 	if (skb_transport_header_was_set(skb))
 		return;
-	else if (skb_flow_dissect_flow_keys(skb, &keys, 0))
+
+	memset(&keys, 0, sizeof(keys));
+	if (__skb_flow_dissect(skb, &flow_keys_buf_dissector, &keys,
+			       0, 0, 0, 0, 0))
 		skb_set_transport_header(skb, keys.control.thoff);
 	else
 		skb_set_transport_header(skb, offset_hint);
diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index 9a074776f70b..e81dab6e9ac6 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -226,6 +226,11 @@ struct flow_dissector {
 	unsigned short int offset[FLOW_DISSECTOR_KEY_MAX];
 };
 
+struct flow_keys_basic {
+	struct flow_dissector_key_control control;
+	struct flow_dissector_key_basic basic;
+};
+
 struct flow_keys {
 	struct flow_dissector_key_control control;
 #define FLOW_KEYS_HASH_START_FIELD basic
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d29f09bc5ff9..ac7b4de4a0f0 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1418,6 +1418,7 @@ struct flow_dissector flow_keys_dissector __read_mostly;
 EXPORT_SYMBOL(flow_keys_dissector);
 
 struct flow_dissector flow_keys_buf_dissector __read_mostly;
+EXPORT_SYMBOL(flow_keys_buf_dissector);
 
 static int __init init_default_flow_dissectors(void)
 {
-- 
2.14.3