Re: test_root reorder(Re: [patch] ext2: Apply Jack's ext3 speedups)

[Jan Kara <jack@suse.cz>]

> Prasanna Meda wrote:
> 
> >   - Folded all three root checkings for 3,  5 and 7 into one loop.
> >   -  Short cut the loop with 3**n < 5 **n < 7**n logic.
> >   -  Even numbers can be ruled out.
> 
> Without going to that complicated path, the better performance
> is achieved with just reordering  of the tests from 3,5,7 to 7,5.3, so
> that average case becomes better. This is more simpler than
>  folding  patch.
  I like a bit more just to reorder the tests (though I agree that your
joined tests for 3,5,7 are probably faster) - it looks much more
readable...

>  Reorder test_root testing from 3,5,7 to 7,5,3 so
>  that average case becomes good. Even number check
>  is added. 
> 
>  Signed-off-by: Prasanna Meda <pmeda@akamai.com>
> 
> --- a/fs/ext3/balloc.c	Fri Jan 28 22:21:45 2005
> +++ b/fs/ext3/balloc.c	Sat Jan 29 02:51:39 2005
> @@ -1451,8 +1451,10 @@
>  {
>  	if (group <= 1)
>  		return 1;
> -	return (test_root(group, 3) || test_root(group, 5) ||
> -		test_root(group, 7));
> +	if (!(group & 1))
> +		return 0;
> +	return (test_root(group, 7) || test_root(group, 5) ||
> +		test_root(group, 3));
>  }
>  
>  /**

								Honza

-- 
Jan Kara <jack@suse.cz>
SuSE CR Labs
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