[dm-devel] Re: IO scheduler based IO Controller V2

[Ryo Tsuruta <ryov valinux co jp>]

Hi Vivek,

> Ryo, dm-ioband breaks the notion of classes and priority of CFQ because
> of FIFO dispatch of buffered bios. Apart from that it tries to provide
> fairness in terms of actual IO done and that would mean a seeky workload
> will can use disk for much longer to get equivalent IO done and slow down
> other applications. Implementing IO controller at IO scheduler level gives
> us tigher control. Will it not meet your requirements? If you got specific
> concerns with IO scheduler based contol patches, please highlight these and
> we will see how these can be addressed.

I'd like to avoid making complicated existing IO schedulers and other
kernel codes and to give a choice to users whether or not to use it.
I know that you chose an approach that using compile time options to
get the same behavior as old system, but device-mapper drivers can be
added, removed and replaced while system is running.

Thanks,
Ryo Tsuruta