Re: [PATCH v3 2/5] mac80211_hwsim: add hashtable with mac address keys for faster lookup

[Johannes Berg <johannes@sipsolutions.net>]

On Wed, 2018-01-10 at 17:42 +0100, Benjamin Beichler wrote:
> This patch adds a rhastable for mac address lookup of hwsim radios. This
> especially improve the speed on reception of a netlink message with a new
> frame. Although redundant, we keep holding a normal list for all radios,
> since the rhashtable_walk interface adds a lot of overhead for iterating
> over all radios and the doc of rhashtable recommend a redundant structure
> for stable walks in such situations.
> 
> Since rhashtable is rcu protected we do not need a lock for delivering
> frames and thus improving this scenario.

Applied, but

> +static u32 hwsim_table_hash(const void *addr, u32 len, u32 seed)
> +{
> +	/* Use last four bytes of hw addr as hash index */
> +	return jhash_1word(*(u32 *)(addr + 2), seed);
> +}

I removed this, because that isn't actually safe - there's only 2-byte
alignment guaranteed... rhashtable will just do jhash() on the whole
thing, which should be fast enough.

johannes