linux-kernel - Re: [RFC PATCH v6 00/12] cxl: Add support for CXL feature commands, CXL device patrol scrub control and DDR5 ECS control features

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Date: Thu, 29 Feb 2024 12:41:53 -0800
From: Tony Luck <tony.luck@...el.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
	Shiju Jose <shiju.jose@...wei.com>,
	"linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
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Subject: Re: [RFC PATCH v6 00/12] cxl: Add support for CXL feature commands,
 CXL device patrol scrub control and DDR5 ECS control features

> Obviously can't talk about who was involved in this feature
> in it's definition, but I have strong confidence it will get implemented
> for reasons I can point at on a public list. 
> a) There will be scrubbing on devices.
> b) It will need control (evidence for this is the BIOS controls mentioned below
>    for equivalent main memory).
> c) Hotplug means that control must be done by OS driver (or via very fiddly
>    pre hotplug hacks that I think we can all agree should not be necessary
>    and aren't even an option on all platforms)
> d) No one likes custom solutions.
> This isn't a fancy feature with a high level of complexity which helps.

But how will users know what are appropriate scrubbing
parameters for these devices?

Car analogy: Fuel injection systems on internal combustion engines
have tweakable controls. But no auto manufacturer wires them up to
a user accessible dashboad control.

Back to computers:

I'd expect the OEMs that produce memory devices to set appropriate
scrubbing rates based on their internal knowledge of the components
used in construction.

What is the use case where some user would need to override these
parameters and scrub and a faster/slower rate than that set by the
manufacturer?

-Tony