Re: [LSF/MM TOPIC] [ATTEND] Throttling I/O

[Tejun Heo <tj@kernel.org>]

Hey,

On Fri, Jan 25, 2013 at 01:26:39PM -0500, Vivek Goyal wrote:
> How many of these spindle drives are not behind some kind of hardware
> raid or on SAN network. Becaue any aggregation of spindle drives by
> hardware/external entity makes group scheduling not worth it very soon.

Hmmm?  Sure, enterprise storage is usually behind some SAN silliness,
but if you go larger scale, e.g. the "cloud" stuff, people usually go
for the most economic solution - ie. some spindles per machine.  At
least the ones I know do.

> > For example, google has been using half-hacky hierarchical writeback
> > support in cfq for quite some time now and they'll switch to upstream
> > implementation once we get it working, so I don't think it's a wasted
> > effort.
> 
> I guess apart from google I have not heard anybody else using it
> successfully and that's when I get skeptic about it. May be once the
> support for buffered write control is in, things will be better. Because,
> that's the biggest offending workload people want to protect against.

Yeah, I think it's mostly because we don't support it and there aren't
too many organizations with enough muscle to implement and maintain
their own hierarchical iosched and mutilations to writeback path.
Given the workloads these servers have to run, some form of io
resource control is just necessary.

Thanks.

-- 
tejun