Re: [PATCH] mm/mempolicy: add sysfs interface to override NUMA node bandwidth

[Yee Li <seven.yi.lee@gmail.com>]

Hi Jonathan,

Thanks for the review.

> As I note below, I'm not convinced this is the best layer to be injecting
> data at if we want a debug interface that allows us to reflect real
> hardware.  Might be the sort of patch that is useful outside the tree though
> so thanks for sharing it!

Perhaps a small tool to compute weights from the desired bandwidth
would be a better approach.

> If it was an SRAT (for GPs) / HMAT issue I'd suggest table injection is
> an adequate way to do testing and debug.
> 
> CDAT is trickier, but maybe we should be thinking about a debug path to inject
> that as well - similar to what we do for ACPI tables.
> 
>  From my point of view I'd rather see debug / testing interfaces that test the
> whole flow rather than just this top layer control.
> 
> However, I can see this is a useful patch for developers. But if you
> are developing debugging bandwidth-aware memory policies, I'm going to assume
> you don't mind building a kernel and adding this patch to make your life
> easier!
> 
> So to me, useful tool but I'm not 'yet' convinced it should be upstream.

You are right, table injection is likely the better approach.
During early hardware development the platform is often unstable, and
firmware may not be able to report it accurately. Letting the OS handle
debugging and evaluate the results can make experimentation easier.

And, thank you for checking the code.