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SubjectRe: [PATCH 2/3]fs/inode: iunique() Optimize Performance
On Wed, Nov 25, 2009 at 07:17:28AM -0700, Matthew Wilcox wrote:
>On Wed, Nov 25, 2009 at 10:12:19PM +0800, Liuweni wrote:
>> @@ -605,8 +605,8 @@ static unsigned long hash(struct super_block *sb, unsigned long hashval)
>> {
>> unsigned long tmp;
>>
>> - tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
>> - L1_CACHE_BYTES;
>> + tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) >>
>> + L1_CACHE_SHIFT;
>> tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
>> return tmp & I_HASHMASK;
>> }
>
>Have you compared the compiler output before/after your change? I'd be
>amazed if GCC isn't able to optimise division-by-a-constant-power-of-two
>into shift-by-constant.

If a compiler can't do this nowadays, I'd consider it's a bug.

--
Live like a child, think like the god.



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