netdev - Re: [PATCH v2 net-next 1/5] net: Get skb hash over flow

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Message-Id: <20150512.103046.1807865055959150687.davem@davemloft.net>
Date:	Tue, 12 May 2015 10:30:46 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	tom@...bertland.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 1/5] net: Get skb hash over flow_keys
 structure

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 11 May 2015 21:56:46 -0700

> On Mon, 2015-05-11 at 20:26 -0700, Tom Herbert wrote:
 ...
> This (2) is not a multiple of 4, so some arches will have unaligned word
> accesses ?
 ...
>> -static __always_inline u32 __flow_hash_3words(u32 a, u32 b, u32 c, u32 keyval)
>> +static __always_inline u32 __flow_hash_words(u32 *words, u32 length, u32 keyval)
>>  {
>> -	return jhash_3words(a, b, c, keyval);
>> +	return jhash2(words, length, keyval);
>> +}
>> +
> 
> -> crash or very slow on MIPS.

Yeah you really can't do this.  You must only pass 4-byte aligned items
into the hash function.
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