buf_ring(9) API precisions

[Robert Watson]

On Thu, 15 Sep 2011, K. Macy wrote:

>> Why are you making an MD guess, the amount of padding to fit the size of a 
>> cache line, in MI API ? Strangely enough, you did not make this assumption 
>> in, say r205488 (picked randomly).
>
> It has been several years, and I haven't done any work in svn in over a 
> year, I don't remember. I probably meant to refine it in a later iteration.
>
> If you would like to send me a patch addressing this I'd be more than happy 
> to apply it if appropriate. Otherwise, I will deal with it some time after 9 
> settles.
>
> Thanks for pointing this out.

I'm not sure if gcc (and friends) allow __aligned(CACHE_LINE_SIZE) to be used 
on individual elements of a struct (causing appropriate padding to be added), 
but that may be one option here.  Of course, that introduces a further 
alignment requirement on the struct itself, so a moderate amount of care would 
need to be used.

Robert