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Subject: Re: Data on hash table probing and memory bandwidth

Author: Matt Taylor

Date: 17:32:17 12/16/02

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On December 16, 2002 at 16:31:21, Robert Hyatt wrote:

>On December 16, 2002 at 16:03:11, Miguel A. Ballicora wrote:
>
>>On December 16, 2002 at 14:51:18, Robert Hyatt wrote:
>>
>>>On December 16, 2002 at 13:32:46, Dieter Buerssner wrote:
>>>
>>>>I did similar tests. IIRC, I got differences of > 5% faster for, what you called
>>>>"new". I unfortunately do not have the code for the "old" (2 different tables)
>>>>handy anymore, to recheck. You are not probing in quiescence search, so it is
>>>>reasonable to expect, that your differences are smaller.
>>>>
>>>>Anyway, for a very small code change (I would guess not more than 1 hour),
>>>>getting 5% is not so bad.
>>>>
>>>>Regards,
>>>>Dieter
>>>
>>>
>>>No, although for me it was 2% which is not so hot...
>>>
>>>I will probably stick with it since it is done, of course....
>>
>>Did you make sure that your table is aligned avery 16 bytes and not 8, for
>>instance?
>>
>>Miguel
>
>
>Yes.  If you look at init.c you will see where I force the starting address to
>be a multiple
>of 16 regardless of what malloc() gives me.
>
>However, my entries are 16 bytes long, and have three in a "set".  No way to map
>a "set" to
>the front of a cache line every time.  It is going to be staggered no matter
>what...

You can if you don't mind bloating the size of the hash by 33%...

-Matt



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