Messages in this thread Patch in this message | | | Date | Tue, 18 Nov 2008 00:41:56 +0100 | From | Eric Dumazet <> | Subject | Re: eth_type_trans(): Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28 |
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Eric Dumazet a écrit : > > But seeing your disassembly, I can see compare_ether_addr() is not inlined. > > This sucks. > > /** > * compare_ether_addr - Compare two Ethernet addresses > * @addr1: Pointer to a six-byte array containing the Ethernet address > * @addr2: Pointer other six-byte array containing the Ethernet address > * > * Compare two ethernet addresses, returns 0 if equal > */ > static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2) > { > const u16 *a = (const u16 *) addr1; > const u16 *b = (const u16 *) addr2; > > BUILD_BUG_ON(ETH_ALEN != 6); > return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])) != 0; > } > > On my machine/compiler, it is inlined, that makes a big difference.
old gcc compiler... OK understood...
> > c0420750 <eth_type_trans>: /* eth_type_trans total: 14417 0.4101 */ > >
Could you try this patch Ingo ?
Thanks
[PATCH] net: eth_type_trans() should be a leaf function
In old days, eth_type_trans() was a leaf function. It is not anymore the case.
eth_type_trans() is a critical network function, called for each incoming packet.
We should make sure it is not calling functions, especially trivial ones.
1) Adds an __always_inline to compare_ether_addr() : This one was created to be faster than memcmp(). It really should be faster (and inlined)
2) Hand code skb_put() call in eth_type_trans()
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> --- include/linux/etherdevice.h | 2 +- net/ethernet/eth.c | 7 ++++++- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h index 25d62e6..94af6a7 100644 --- a/include/linux/etherdevice.h +++ b/include/linux/etherdevice.h @@ -128,7 +128,7 @@ static inline void random_ether_addr(u8 *addr) * * Compare two ethernet addresses, returns 0 if equal */ -static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2) +static __always_inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2) { const u16 *a = (const u16 *) addr1; const u16 *b = (const u16 *) addr2; diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c index b9d85af..30b60b2 100644 --- a/net/ethernet/eth.c +++ b/net/ethernet/eth.c @@ -162,7 +162,12 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev) skb->dev = dev; skb_reset_mac_header(skb); - skb_pull(skb, ETH_HLEN); + /* + * Hand coded skb_pull(skb, ETH_HLEN) to avoid a function call + */ + if (likely(skb->len >= ETH_HLEN)) + __skb_pull(skb, ETH_HLEN); + eth = eth_hdr(skb); if (is_multicast_ether_addr(eth->h_dest)) { | |