linux-kernel - Re: eth_type_trans(): Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

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Date:	Tue, 18 Nov 2008 00:41:56 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, rjw@...k.pl,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	cl@...ux-foundation.org, efault@....de, a.p.zijlstra@...llo.nl,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: eth_type_trans(): Re: [Bug #11308] tbench regression on each
 kernel release from 2.6.22 -&gt; 2.6.28

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@...mosbay.com>
---
 include/linux/etherdevice.h |    2 +-
 net/ethernet/eth.c          |    7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

View attachment "eth_type_trans_speedup.patch" of type "text/plain" (1054 bytes)