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[dm-devel] Re: IO scheduler based IO controller V10



On Fri, Oct 02 2009, Mike Galbraith wrote:
> On Fri, 2009-10-02 at 07:24 -0700, Linus Torvalds wrote:
> > 
> > On Fri, 2 Oct 2009, Jens Axboe wrote:
> > > 
> > > It's really not that simple, if we go and do easy latency bits, then
> > > throughput drops 30% or more.
> > 
> > Well, if we're talking 500-950% improvement vs 30% deprovement, I think 
> > it's pretty clear, though. Even the server people do care about latencies. 
> > 
> > Often they care quite a bit, in fact.
> > 
> > And Mike's patch didn't look big or complicated.
> 
> But it is a hack.  (thought about and measured, but hack nonetheless)
> 
> I haven't tested it on much other than reader vs streaming writer.  It
> may well destroy the rest of the IO universe. I don't have the hw to
> even test any hairy chested IO.

I'll get a desktop box going on this too. The plan is to make the
latency as good as we can without making too many stupid decisions in
the io scheduler, then we can care about the throughput later. Rinse
and repeat.

-- 
Jens Axboe


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