netdev - Re: [PATCH net-next] etherdevice: Optimize compare_ether_addr/ether_addr

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Date:	Sat, 31 Aug 2013 09:43:08 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] etherdevice: Optimize
 compare_ether_addr/ether_addr_equal

On Sat, 31 Aug 2013 01:54:16 -0700
Joe Perches <joe@...ches.com> wrote:

> When CONFIG_HAS_EFFICIENT_UNALIGNED_ACCESS is set,
> optimize compare_ether_addr a little by removing an
> xor and or by using a u32 and u16 comparison
> instead of 3 separate u16 comparisons.
> 
> Make the ether_addr_equal_64bits code a bit simpler
> by adding a test for CONFIG_64BIT and calling
> ether_addr_equal otherwise.
> 
> This also slightly improves ether_addr_equal_64bits
> by removing the zap_last_2bytes shifts in the !64bit
> case.
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
>  include/linux/etherdevice.h | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
> index c623861..2514d17 100644
> --- a/include/linux/etherdevice.h
> +++ b/include/linux/etherdevice.h
> @@ -208,11 +208,19 @@ static inline void eth_hw_addr_random(struct net_device *dev)
>   */
>  static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2)
>  {
> +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +	u32 fold = ((*(const u32 *)addr1) ^ (*(const u32 *)addr2));
> +	fold |= ((*(const u16 *)(addr1 + 4)) ^ (*(const u16 *)(addr2 + 4)));
> +
> +	BUILD_BUG_ON(ETH_ALEN != 6);
> +	return fold != 0;
> +#else
>  	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;
> +#endif
>  }
>  

If you really want to be efficient do it as one 64 bit mask and compare.
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