Re: [PATCH block-5.14] Revert "block/mq-deadline: Add cgroup support"

[Tejun Heo <tj@kernel.org>]

On Fri, Aug 13, 2021 at 10:17:42AM -0700, Bart Van Assche wrote:
> On 8/13/21 9:29 AM, Tejun Heo wrote:
> > The problem with complex optional hardware features is often the
> > accompanying variability in terms of availability, reliability and
> > behavior. The track record has been pretty sad. That isn't to say this
> > won't be useful for anybody but it'd need careful coordination in
> > terms of picking hardware vendor and model and ensuring vendor
> > support, which kinda severely limits the usefulness.
> 
> I think the above view is too negative. Companies that store large amounts
> of data have the power to make this happen by only buying storage devices
> that support I/O prioritization well enough.

The problem usually is that there always are other ways to skin that
cat which don't depend on having complex optional features. So, the
comparison isn't just about or among devices that support such extra
feature but with other solutions which don't need them in the first
place. Throw in the many inherent problems in expanding hardware
interface such as variability and timescale mismatch (hardware changes
a lot faster than software stack), the long term result tends to skew
pretty clearly.

Thanks.

-- 
tejun