Re: [PATCH 2/5] writeback: dirty position control

[Peter Zijlstra]

On Tue, 2011-08-09 at 19:20 +0200, Peter Zijlstra wrote:
> 
> Now all of the above would seem to suggest:
> 
>   dirty_ratelimit := ref_bw
> 
> However for that you use:
> 
>   if (pos_bw < dirty_ratelimit && ref_bw < dirty_ratelimit)
>         dirty_ratelimit = max(ref_bw, pos_bw);
> 
>   if (pos_bw > dirty_ratelimit && ref_bw > dirty_ratelimit)
>         dirty_ratelimit = min(ref_bw, pos_bw);
> 
> You have:
> 
>   pos_bw = dirty_ratelimit * pos_ratio
> 
> Which is ref_bw without the write_bw/dirty_bw factor, this confuses me..
> why are you ignoring the shift in output vs input rate there? 

Could you elaborate on this primary feedback loop? Its the one part I
don't feel I actually understand well.


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