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Re: [PATCH 3/9] Use murmurhash3 for pointer map hashing


On Mon, Apr 22, 2013 at 5:42 PM, Andi Kleen <ak@linux.intel.com> wrote:
> On Mon, Apr 22, 2013 at 01:46:58PM +0200, Richard Biener wrote:
>> On Fri, Apr 19, 2013 at 11:31 PM, Andi Kleen <andi@firstfloor.org> wrote:
>> > From: Andi Kleen <ak@linux.intel.com>
>> >
>> > For a large LTO test case The previous pointer hash change brought
>> > the collision rate for the WPA gimple type hash table from 90% to
>> > 70. This patch uses the well known murmur3 to improve it further
>> > to 64%.
>>
>> But if they are pointers then pointer_hash should be good enough... ?
>
> The original pointer hash (ptr >> 3) % hashsize and throwing away most bits is
> very poor.
>
> The evahash based on I sent earlier is better, but murmur3 is even better than
> that, at least for this case.

I'd rather not have different pointer hashes for things where there isn't a
fundamental difference between the pointer values.

Richard.

> -Andi
>


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