Re: [PATCH 06/16] SUPPORT.md: Add scalability features

[Julien Grall <julien.grall@linaro.org>]

Hi George,

On 13/11/17 15:41, George Dunlap wrote:
> Superpage support and PVHVM.
> 
> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
> ---
> CC: Ian Jackson <ian.jackson@citrix.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Jan Beulich <jbeulich@suse.com>
> CC: Stefano Stabellini <sstabellini@kernel.org>
> CC: Konrad Wilk <konrad.wilk@oracle.com>
> CC: Tim Deegan <tim@xen.org>
> CC: Julien Grall <julien.grall@arm.com>
> ---
>   SUPPORT.md | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/SUPPORT.md b/SUPPORT.md
> index c884fac7f5..a8c56d13dd 100644
> --- a/SUPPORT.md
> +++ b/SUPPORT.md
> @@ -195,6 +195,27 @@ on embedded platforms.
>   
>   Enables NUMA aware scheduling in Xen
>   
> +## Scalability
> +
> +### 1GB/2MB super page support
> +
> +    Status, x86 HVM/PVH: : Supported
> +    Status, ARM: Supported
> +
> +NB that this refers to the ability of guests
> +to have higher-level page table entries point directly to memory,
> +improving TLB performance.
> +This is independent of the ARM "page granularity" feature (see below).

I am not entirely sure about this paragraph for Arm. I understood this 
section as support for stage-2 page-table (aka EPT on x86) but the 
paragraph lead me to believe to it is for guest.

The size of super pages of guests will depend on the page granularity 
used by itself and the format of the page-table (e.g LPAE vs short 
descriptor). We have no control on that.

What we have control is the size of mapping used for stage-2 page-table.

> +
> +### x86/PVHVM
> +
> +    Status: Supported
> +
> +This is a useful label for a set of hypervisor features
> +which add paravirtualized functionality to HVM guests
> +for improved performance and scalability.
> +This includes exposing event channels to HVM guests.
> +
>   # Format and definitions
>   
>   This file contains prose, and machine-readable fragments.
> 

Cheers,

-- 
Julien Grall

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