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

[Linus Torvalds <torvalds linux-foundation org>]

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. 

> You can't say it's black and white latency vs throughput issue,

Umm. Almost 1000% vs 30%. Forget latency vs throughput. That's pretty damn 
black-and-white _regardless_ of what you're measuring. Plus you probably 
made up the 30% - have you tested the patch?

And quite frankly, we get a _lot_ of complaints about latency. A LOT. It's 
just harder to measure, so people seldom attach numbers to it. But that 
again means that when people _are_ able to attach numbers to it, we should 
take those numbers _more_ seriously rather than less.

So the 30% you threw out as a number is pretty much worthless. 

		Linus