On Fri, Aug 26, 2011 at 08:20:57PM +0800, Wu Fengguang wrote:
> On Fri, Aug 26, 2011 at 08:11:50PM +0800, Peter Zijlstra wrote:
> > On Fri, 2011-08-26 at 19:26 +0800, Wu Fengguang wrote:
> > > Now I get 3 figures. Test case is: run 1 dd write task for 300s, with
> > > a "disturber" dd read task during roughly 120-130s. 
> > 
> > Ah, but ideally the disturber task should run in bursts of 100ms
> > (<feedback period), otherwise your N is indeed mostly constant.
> 
> Ah yeah, the disturber task should be a dd writer! Then we get
> 
> - 120s: N=1 => N=2
> - 130s: N=2 => N=1

Here they are. The write disturber starts/stops around 150s.

We got similar result as in the read disturber case, even though one
disturbs N and the other impacts writeout bandwith.  The original
patchset is consistently performing much better :)

Thanks,
Fengguang