Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: hashed waitqueues | Date | Sat, 5 Jan 2002 01:37:40 +0100 |
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On January 4, 2002 06:40 pm, William Lee Irwin III wrote:
> + unsigned long hash = (unsigned long)page;
Just to be anal here, 'long' doesn't add anything useful to this declaration. In fact, u32 is what you want since you've chosen your multiplier with a 32 bit register in mind - on 64bit arch I think you'll get distinctly non-random results as it stands.
> + hash *= GOLDEN_RATIO_PRIME; > + hash >>= BITS_PER_LONG - zone->wait_table_bits; > + hash &= zone->wait_table_size - 1;
Nice hash! For arches with expensive multiplies you might want to look for a near-golden ratio multiplier that has a simple contruction in terms of 1's & 0's so it can be computed with 2 or 3 shift-adds, dumping the efficiency problem on the compiler. You don't have to restrict your search to the neighbourhood of 32 bits, you can go a few bits less than that and substract from a smaller value than BITS_PER_LONG (actually, you should just write '32' there, since that's what you really have in mind).
-- Daniel
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