lkml.org 
[lkml]   [2009]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    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.



    \
     
     \ /
      Last update: 2009-11-25 15:47    [W:0.032 / U:29.164 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site