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[dm-devel] Re: Do not overload dispatch queue (Was: Re: IO scheduler based IO controller V10)



On Sat, 2009-10-03 at 21:07 +0200, Mike Galbraith wrote:
> On Sat, 2009-10-03 at 19:35 +0200, Jens Axboe wrote:

> > So that's pure goodness, at least.
> 
> Yeah, but it's a double edged sword, _maybe_ cut too far in the other
> direction.  (impression)
> 
> > > perf stat testo.sh                               Avg
> > > 108.12   106.33    106.34    97.00    106.52   104.8  1.000 fairness=0 overload_delay=0
> > >  93.98   102.44     94.47    97.70     98.90    97.4   .929 fairness=0 overload_delay=1
> > >  90.87    95.40     95.79    93.09     94.25    93.8   .895 fairness=1 overload_delay=0
> > >  89.93    90.57     89.13    93.43     93.72    91.3   .871 fairness=1 overload_delay=1
> > >  89.81    88.82     91.56    96.57     89.38    91.2   .870 desktop=1 +last_end_sync
> > >  92.61    94.60     92.35    93.17     94.05    93.3   .890 block-for-linus
> > 
> > Doesn't look too bad, all things considered. Apart from "stock" cfq,
> > it's consistent. And being consistent is a Good Thing. Performance wise,
> > it's losing out to "stock" but looks pretty competetive otherwise.
> 
> No, not bad at all, still a large win over stock.
> 
> > So far that looks like a winner. The dictator wanted good latency, he's
> > getting good latency. I'll continue working on this on monday, while I'm
> > waiting for delivery of the Trabant.
> 
> I'm unsure feel wise.  Disk is sounding too seeky, which worries me.

But, this is a _huge_ improvement of the dd vs reader thing regardless
of any further tweaking that may or may not prove necessary.  That ages
old corner case seems to be defeated.

	-Mike


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