Re: [Qemu-ppc] [PATCHv3 2/5] pseries: Stubs for HPT resizing

[David Gibson]

On Tue, Dec 13, 2016 at 03:29:05PM +0100, Laurent Vivier wrote:
> 
> 
> On 12/12/2016 05:06, David Gibson wrote:
> > This introduces stub implementations of the H_RESIZE_HPT_PREPARE and
> > H_RESIZE_HPT_COMMIT hypercalls which we hope to add in a PAPR
> > extension to allow run time resizing of a guest's hash page table.  It
> > also adds a new machine property for controlling whether this new
> > facility is available, and logic to check that against availability
> > with KVM (only supported with KVM PR for now).
> > 
> > Finally, it adds a new string to the hypertas property in the device
> > tree, advertising to the guest the availability of the HPT resizing
> > hypercalls.  This is a tentative suggested value, and would need to be
> > standardized by PAPR before being merged.
> 
> Could you explain somewhere what is the aim of the "flags" parameter?
> It could help to understand why we have it as it is not used.

It's mostly just there on the general principle that have some way of
extending is a good idea.

As an example of a possible extension, we could have a flag which
caused all the valid HPTEs to be rehashed, instead of just the bolted
ones - we'd need to do tests to see if that was worthwhile (probably a
tradeoff between commit downtime and post-resize performance).

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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