Re: [PATCH v3 01/18] block: introduce duration-limits priority class

Martin K. Petersen
2023-01-31T02:50:22Z

Damien,

> Makes sense. Though I think it will be hard to define a set of QoS
> hints that are useful for a wide range of applications, and even
> harder to convert the defined hint classes to CDL descriptors. I fear
> that we may end up with the same issues as IO hints/streams.

Hints mainly failed because non-Linux OSes had very different
expectations about how this was going to work. So that left device
vendors in a situation where they had to essentially support 3 different
approaches all implemented using the same protocol.

The challenge of being a general purpose OS is to come up with concepts
that are applicable in a variety of situations. Twiddling protocol
fields is the easy part.

I have a couple of experienced CDL users that I'd like to talk to and
try to get a better idea of what a suitable set of defaults might look
like.

> This hint applies to all priority classes and levels, that is, for the
> CDL case, we can enrich any priority with a hint that specifies the
> CDL index to use for an IO.

Yeah, I like that approach better.

--
Martin K. Petersen Oracle Linux Engineering