N-way mirror read speedup in zfsonlinux

[Steven Hartland]

----- Original Message ----- 
From: "Matthew Ahrens" 
> On Sat, Aug 17, 2013 at 8:08 PM, Steven Hartland wrote:
> 
>> 2) do {} while() loops have their place, but only if they improve
>>>   code clarity and/or yield a significant performance benefit.  I
>>>   don't see either applying here.
>>>
>>
>> I'd have to disagree, unless using it makes it difficult to understand,
>> a do while should be used is when you know there's always going to be
>> one iteration of the loop and hence no need to test before performing
>> the first iteration.
>>
> 
> 
> I agree with Justin.  This nonstandard iteration makes it more difficult to
> understand.  I would expect there is no measurable performance benefit,
> either.

I'd like to understand why its more difficult to understand?

Its not like its a none standard language construct, its already used in
the code base in lots of place e.g.

uts/common/zmod/deflate.c:
do {...} while (--len > 0);
uts/common/dtrace/dtrace.c:
do {...} } while (--length != 0);

Compared to this case:
do {...} while (--c >= 0);

Yes its only saving one comparison per call but thats exactly what it
was added to language to do.

Not trying to be be a pain, I'm just trying to understand why using the
correct code for the job is confusing?

    Regards
    Steve

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