linux-kernel - Re: [RFC v3 1/7] hashtable: introduce a small and naive hashtable

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Date:	Tue, 07 Aug 2012 11:49:41 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Josh Triplett <josh@...htriplett.org>
CC:	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, paul.gortmaker@...driver.com,
	davem@...emloft.net, rostedt@...dmis.org, mingo@...e.hu,
	ebiederm@...ssion.com, aarcange@...hat.com, ericvh@...il.com,
	netdev@...r.kernel.org, eric.dumazet@...il.com,
	mathieu.desnoyers@...icios.com
Subject: Re: [RFC v3 1/7] hashtable: introduce a small and naive hashtable

On 08/07/2012 04:55 AM, Josh Triplett wrote:
> On Tue, Aug 07, 2012 at 02:45:10AM +0200, Sasha Levin wrote:
>> +/**
>> + * hash_add - add an object to a hashtable
>> + * @hashtable: hashtable to add to
>> + * @bits: bit count used for hashing
>> + * @node: the &struct hlist_node of the object to be added
>> + * @key: the key of the object to be added
>> + */
>> +#define hash_add(hashtable, bits, node, key)				\
>> +	hlist_add_head(node, &hashtable[hash_min(key, bits)]);
> 
> Any particular reason to make this a macro rather than a static inline?

Yes. As Eric Dumazet pointed out, hash_64() is slower than hash_32() so we should be calling hash_32() if possible (if key size is 32bits long).

This way we can call hash_min() without knowing the key size. See also the definition of hash_min() above.



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