Re: [PATCH v5 24/29] x86/resctrl: Add energy/perf choices to rdt boot option

[Fenghua Yu]

Hi, Tony,

On 5/21/25 15:50, Tony Luck wrote:
> Users may want to force either of the telemetry features on
> (in the case where they are disabled due to erratum) or off
> (in the case that a limited number of RMIDs for a telemetry
> feature reduces the number of monitor groups that can be
> created.)
>
> Unlike other options that are tied to X86_FEATURE_* flags,
> these must be queried by name. Add a function to do that.
>
> Add checks for users who forced either feature off.
>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
>   .../admin-guide/kernel-parameters.txt         |  2 +-
>   arch/x86/kernel/cpu/resctrl/internal.h        |  4 +++
>   arch/x86/kernel/cpu/resctrl/core.c            | 28 +++++++++++++++++++
>   arch/x86/kernel/cpu/resctrl/intel_aet.c       |  6 ++++
>   4 files changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index d9fd26b95b34..4811bc812f0f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5988,7 +5988,7 @@
>   	rdt=		[HW,X86,RDT]
>   			Turn on/off individual RDT features. List is:
>   			cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
> -			mba, smba, bmec.
> +			mba, smba, bmec, energy, perf.
>   			E.g. to turn on cmt and turn off mba use:
>   				rdt=cmt,!mba
>   
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 42da0a222c7c..524f3c183900 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -167,6 +167,10 @@ void __init intel_rdt_mbm_apply_quirk(void);
>   
>   void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
>   
> +bool rdt_is_option_force_enabled(char *option);
> +
> +bool rdt_is_option_force_disabled(char *option);
> +
>   bool intel_aet_get_events(void);
>   void __exit intel_aet_exit(void);
>   int intel_aet_read_event(int domid, int rmid, enum resctrl_event_id evtid, u64 *val);
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index f07f5b58639a..b23309566500 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -797,6 +797,8 @@ enum {
>   	RDT_FLAG_MBA,
>   	RDT_FLAG_SMBA,
>   	RDT_FLAG_BMEC,
> +	RDT_FLAG_ENERGY,
> +	RDT_FLAG_PERF,
>   };
>   
>   #define RDT_OPT(idx, n, f)	\
> @@ -822,6 +824,8 @@ static struct rdt_options rdt_options[]  __ro_after_init = {
>   	RDT_OPT(RDT_FLAG_MBA,	    "mba",	X86_FEATURE_MBA),
>   	RDT_OPT(RDT_FLAG_SMBA,	    "smba",	X86_FEATURE_SMBA),
>   	RDT_OPT(RDT_FLAG_BMEC,	    "bmec",	X86_FEATURE_BMEC),
> +	RDT_OPT(RDT_FLAG_ENERGY,    "energy",	0),
> +	RDT_OPT(RDT_FLAG_PERF,	    "perf",	0),

Boot options "energy" and "perf" are PMT event groups level. Other boot 
options are individual event level.

E.g. "!perf" forces off all 7 PMT PERF events.

e.g. "uops retired" event has an erratum but all other PERF events work 
fine. Disabling "perf" group disables all PERF events. Is "!perf" a 
useful boot option?

Is there any consideration to have boot options at PMT event group level 
instead of individual PMT event level like legacy events?

[SNIP]

Thanks.

-Fenghua