[dm-devel] Re: Regarding dm-ioband tests

[Ryo Tsuruta <ryov valinux co jp>]

Hi Vivek,

Vivek Goyal <vgoyal redhat com> wrote:
> > In addition,
> > there are devices which doesn't use standard IO schedulers, and
> > dm-ioband can work on even such devices.
> 
> This is a interesting use case. Few thoughts.
> 
> - Can't io scheduling mechanism of these devices make use of elevator and
>   elevator fair queuing interfaces to take advantage of io controlling
>   mechanism. It should not be too difficult. Look at noop. It has
>   just 131 lines of code and it now supports hierarchical io scheduling.
>  
>   This will come with request queue and its merging and plug/unplug
>   mechanism. Is that an issue?
>
> - If not, then yes, for these corner cases, io scheduler based controller
>   does not work as it is.

I have a extreme fast SSD and its device driver provides its own
make_request_fn(). So the device driver intercepts IO requests and the
subsequent processes are done within it.

Thanks,
Ryo Tsuruta