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From: David Miller <davem@davemloft.net>
To: mirqus@gmail.com
Cc: roland@purestorage.com, johnwheffner@gmail.com, mj@ucw.cz,
	netdev@vger.kernel.org
Subject: Re: [PATCH 1/2] neigh: Store hash shift instead of mask.
Date: Mon, 11 Jul 2011 14:08:28 -0700 (PDT)	[thread overview]
Message-ID: <20110711.140828.1179960343630781204.davem@davemloft.net> (raw)
In-Reply-To: <CAHXqBFLk5ze9y7htyO+9z7=qcznNjXeuJK5Rs1t2ym=vLqDy5Q@mail.gmail.com>

From: Michał Mirosław <mirqus@gmail.com>
Date: Mon, 11 Jul 2011 13:58:41 +0200

> 2011/7/11 David Miller <davem@davemloft.net>:
>> And mask the hash function result by simply shifting
>> down the "->hash_shift" most significant bits.
>>
>> Currently which bits we use is arbitrary since jhash
>> produces entropy evenly across the whole hash function
>> result.
>>
>> But soon we'll be using universal hashing functions,
>> and in those cases more entropy exists in the higher
>> bits than the lower bits, because they use multiplies.
> 
> You could use some evil shift tricks to cut some instructions if you like. ;-)

If these were fast paths I would seriously consider it :-)

But they really are not.

      reply	other threads:[~2011-07-11 21:08 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-11  8:48 [PATCH 1/2] neigh: Store hash shift instead of mask David Miller
2011-07-11 11:58 ` Michał Mirosław
2011-07-11 21:08   ` David Miller [this message]

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