Re: [PATCH v4 09/10] x86/resctrl: Add arch_has_{sparse,empty}_bitmaps to explain CAT differences

[Reinette Chatre]

Hi James,

On 5/26/2020 6:40 AM, James Morse wrote:
> Intel CPUs expect the cache bitmap provided by user-space to have on
> a single span of 1s, whereas AMD can support bitmaps like 0xf00f.
> Arm's MPAM support also allows sparse bitmaps.
> 
> Similarly, Intel CPUs check at least one bit set, whereas AMD CPUs
> are quite happy with an empty bitmap. Arm's MPAM allows an empty
> bitmap.
> 
> To move resctrl out to /fs/ we need to explain platform differences
> like this. Add two resource properties arch_has_{empty,sparse}_bitmaps.
> Test these around the relevant parts of cbm_validate().
> 
> Merging the validate calls causes AMD to gain the min_cbm_bits test
> needed for Haswell, but as it always sets this value to 1, it will
> never match.
> 
> CC: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Reviewed-by: Babu Moger <babu.moger@xxxxxxx>

Thank you for adding handling of empty bitmaps.

Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>

Reinette