netdev - Re: [v2 PATCH 3/10] rhashtable: Allow hashfn to be unset

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Date:	Sun, 22 Mar 2015 11:55:05 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	Josh Triplett <josh@...htriplett.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	netdev@...r.kernel.org
Subject: Re: [v2 PATCH 3/10] rhashtable: Allow hashfn to be unset

On 03/22/15 at 07:04pm, Herbert Xu wrote:
> @@ -134,6 +136,7 @@ struct rhashtable {
>  	struct bucket_table __rcu	*tbl;
>  	atomic_t			nelems;
>  	bool                            being_destroyed;
> +	unsigned int			key_len;

Why is this needed? It looks like you're always initializing this
with ht->p.key_len

>  	struct rhashtable_params	p;
>  	struct work_struct		run_work;
>  	struct mutex                    mutex;
> @@ -199,12 +202,30 @@ static inline unsigned int rht_key_hashfn(
>  	struct rhashtable *ht, const struct bucket_table *tbl,
>  	const void *key, const struct rhashtable_params params)
>  {
> -	unsigned key_len = __builtin_constant_p(params.key_len) ?
> -			   (params.key_len ?: ht->p.key_len) :
> -			   params.key_len;
> +	unsigned hash;

unsigned int

In several places as well

> +	if (!__builtin_constant_p(params.key_len))
> +		hash = ht->p.hashfn(key, ht->key_len, tbl->hash_rnd);

I don't understand this. It looks like you only consider
params->key_len if it's constant.

> +	else if (params.key_len) {
> +		unsigned key_len = params.key_len;
> +
> +		if (params.hashfn)
> +			hash = params.hashfn(key, key_len, tbl->hash_rnd);
> +		else if (key_len & (sizeof(u32) - 1))
> +			hash = jhash(key, key_len, tbl->hash_rnd);
> +		else
> +			hash = jhash2(key, key_len / sizeof(u32),
> +				      tbl->hash_rnd);
> +	} else {
> +		unsigned key_len = ht->p.key_len;
> +
> +		if (params.hashfn)
> +			hash = params.hashfn(key, key_len, tbl->hash_rnd);
> +		else
> +			hash = jhash(key, key_len, tbl->hash_rnd);

Why don't we opt-in to jhash2 in this case?
--
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