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

[Ingo Molnar <mingo elte hu>]

* Jens Axboe <jens axboe oracle com> wrote:

> It's not hard to make the latency good, the hard bit is making sure we 
> also perform well for all other scenarios.

Looking at the numbers from Mike:

 | dd competing against perf stat -- konsole -e exec timings, 5 back to 
 | back runs
 |                                                         Avg
 | before         9.15    14.51     9.39    15.06     9.90   11.6
 | after [+patch] 1.76     1.54     1.93     1.88     1.56    1.7

_PLEASE_ make read latencies this good - the numbers are _vastly_ 
better. We'll worry about the 'other' things _after_ we've reached good 
latencies.

I thought this principle was a well established basic rule of Linux IO 
scheduling. Why do we have to have a 'latency vs. bandwidth' discussion 
again and again? I thought latency won hands down.

	Ingo