Re: [PATCH v10 04/17] x86/resctrl: Honor rdt=perf option to force enable AET perf events

[Reinette Chatre]

Hi Tony,

On 7/29/26 10:27 AM, Tony Luck wrote:
> resctrl can disable ("force_off") a feature supported by the platform if,
> for example, there is an erratum related to the feature or, in the case of AET
> (Application Energy Telemetry), when the event group has insufficient RMIDs. The
> "rdt=" kernel command line option lets the user override ("force_on") when
> a feature is disabled in such case. Users may also disable ("force_off")
> individual supported resctrl features they do not need.
> 
> Linux enumerates AET once on first mount and skips this enumeration if
> the associated event group is supported but disabled. Since AET is only
> enumerated once, this check is guaranteed to only consider disabling via
> the rdt= kernel parameter.
> 
> However, when transitioning to enumerate AET on every mount, it is no longer
> correct to skip enumeration simply because an event group is marked as
> disabled. It is then possible for resctrl to have force-disabled the event
> group during an earlier enumeration due to insufficient RMIDs, which would
> improperly cause the kernel to ignore a user's explicit rdt= override on
> subsequent mounts.
> 
> Ensure the user's command line choices take precedence over system-level limits.
> 
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---

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

Reinette