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From: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Date: Tue, 24 Feb 2015 01:15:08 +0300
Message-ID: <CAHNKnsTpYEdkF9OETnjKua9bOb4=-MXC26pctUvJW0gFJAUS1g@mail.gmail.com> (sfid-20150223_231548_970707_5311BF8A)
Subject: Re: [RFC] mac80211: use rhashtable for station table
To: Johannes Berg <johannes@sipsolutions.net>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	Thomas Graf <tgraf@suug.ch>
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Sender: linux-wireless-owner@vger.kernel.org

2015-02-24 1:07 GMT+03:00 Johannes Berg <johannes@sipsolutions.net>:
> On Mon, 2015-02-23 at 23:01 +0100, Johannes Berg wrote:
>> On Mon, 2015-02-23 at 22:52 +0100, Johannes Berg wrote:
>>
>> > We also can't rely on 4-byte alignment though, so perhaps we should do
>> > something like
>> >
>> > u32 sta_info_hash(void *addr, u32 len, u32 seed)
>> > {
>> >     u16 *a = addr;
>> >
>> >     return jhash_3words(a[0], a[1], a[2], seed);
>> > }
>>
>> Or better do
>>
>>       return jhash_2words(addr[0], (addr[1] << 16) | addr[2], seed);
>>
>> since I have no idea how the missing high 16 bits would behave.
>> (we can rely on 2-byte alignment, but not 4-byte)
>
> Actually, we cannot rely on alignment, so we need to do this:
>
> static u32 sta_addr_hash(const void *key, u32 length, u32 seed)
> {
>         return jhash(key, ETH_ALEN, seed);
> }
>
> which still generates better code since the compiler can optimise based
> on the fixed length.
>
Nice catch!

-- 
Sergey