N-way mirror read speedup in zfsonlinux

[Steven Hartland]

Baring any more feedback I intend to commit this soon, so please shout
if there's anything outstanding ;-)

----- Original Message ----- 
From: "Steven Hartland"
> ----- Original Message ----- 
> From: "Matthew Ahrens" <mahrens at delphix.com>
> 
> 
>> The platform-independent code in the patch looks good to me with one
>> exceptions:
>> 
>>  mm->mm_children = c--;
>>
>> It's non-obvious why c should be decremented *here*, as opposed to as part
>> of the loop logic.  If there's some trick going on with the loop then it's
>> lost on me.
> 
> This just configures 'c' so the loop starts with the last child, could split
> to a c--; on its own line if people prefer?
> 
>> Does it matter that we go through the children in reverse
>> order?  Is there something wrong with the existing loop logic:
>> 
>>  for (c = 0; c < mm->mm_children; c++) {
> 
> Order is not important, but using a do{} while(); provides a small optimisation
> which avoids the first loop test totally and then on subisquent iterations
> compare against a constant not through a struct pointer.

    Regards
    Steve

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