Re: [PATCH v14 10/24] x86/resctrl: Honor rdt={perf|energy} options to force enable AET events

[Chen Yu]

On Mon, Oct 19, 2026 at 01:50:17PM -0700, Tony Luck wrote:
> resctrl can disable a feature the platform supports, for example because
> of an erratum or, for Application Energy Telemetry (AET), because an event
> group has insufficient RMIDs. The "rdt=" kernel command line option lets
> the user force such a feature on anyway, and also lets the user disable
> supported features they do not need.
> 
> resctrl enumerates AET once, on first mount. Enumeration skips an event
> group that is marked disabled. An event group with insufficient RMIDs is
> marked disabled even when the user forced it on, but this happens after
> the test for forced off when enumeration begins for an event group.
> 
> This will be broken when AET is enumerated on every mount. The disable mark
> recorded for insufficient RMIDs on one mount causes the event group to be
> skipped on the next, ignoring the user's explicit rdt= request to enable it.
> 
> In preparation for enumerating AET on every mount, skip a disabled event
> group only if the user has not forced it on. As a result, when the command
> line both disables and enables the same event group, for example
> "rdt=!perf,perf:<guid>", enabling now takes precedence. This matches how
> rdt= handles the other resctrl features.
> 
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> v14:
> 	New commit message. Dropped previous supplied Reinette RB tag.
> ---
>  arch/x86/kernel/cpu/resctrl/intel_aet.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> index 66cd8c2c7a51..9f0829a82cb0 100644
> --- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
> +++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> @@ -262,7 +262,7 @@ static bool enable_events(struct event_group *e, struct pmt_feature_group *p)
>  	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_PERF_PKG].r_resctrl;
>  	int skipped_events = 0;
>  
> -	if (e->force_off)
> +	if (e->force_off && !e->force_on)
>  		return false;
>

OK, it seems that the user always has the highest priority in deciding whether
this event is enabled, which overrides the hardware/kernel decision. This will also
be the design for region aware MBA's erdt:3waymba. Per my understanding,

Reviewed-by: Chen Yu <yu.c.chen@xxxxxxxxx>

thanks,
Chenyu

>  	if (!group_has_usable_regions(e, p))
> -- 
> 2.56.0
>