Re: [PATCH v8 17/32] x86/resctrl: Discover hardware telemetry events

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Tony,

On 8/11/25 11:16 AM, Tony Luck wrote:
> Data for telemetry events is collected by each CPU and sent

"Each CPU collects data for telemetry events that it sends ..."
(imperative)

> to a nearby telemetry event aggregator either when the value
> of IA32_PQR_ASSOC.RMID is changed, or when two milliseconds

"is changed" -> "changes"
"or when a two millisecond timer expires" (imperative and 
matches the cover letter ... almost ... there is timer vs counter)

> have elapsed.

Please make use of allowed line length. These line wraps are getting very
short and quite noticeable with this growing changelog.

> 
> The telemetry event aggregators maintain per-RMID per-event
> counts of the total seen for all the CPUs. There may be more
> than one telemetry event aggregator per package.
> 
> Each telemetry event aggregator is responsible for a specific
> group of events. E.g. on the Intel Clearwater Forest CPU there
> are two types of aggregators. One type tracks a pair of energy
> related events. The other type tracks a subset of "perf" type
> events.
> 
> The event counts are made available to Linux in a region of
> MMIO space for each aggregator. All details about the layout
> of counters in each aggregator MMIO region are described in
> XML files published by Intel and mad available in a GitHub

"mad" -> "made"

> repository: https://github.com/intel/Intel-PMT.
> 
> The key to matching a specific telemetry aggregator to the
> XML file that describes the MMIO layout is a 32-bit value. The
> Linux telemetry subsystem refers to this as a "guid" while
> the XML files call it a "uniqueid".
> 
> Each XML file provides the following information:
> 1) Which telemetry events are included in the group.
> 2) The order in which the event counters appear for each RMID.
> 3) The value type of each event counter (integer or fixed-point).
> 4) The number of RMIDs supported.
> 5) Which additional aggregator status registers are included.
> 6) The total size of the MMIO region for this aggregator.
> 
> Enumeration of support for telemetry events is done by the
> INTEL_PMT_DISCOVERY driver (a subcomponent of the INTEL_PMT_TELEMETRY

"The INTEL_PMT_TELEMETRY driver enumerates support for telemetry events."
(imperative)
Could mentions of INTEL_PMT_DISCOVERY be dropped? It is 
INTEL_PMT_TELEMETRY that provides intel_pmt_get_regions_by_feature()
and I do not see how describing INTEL_PMT_DISCOVERY helps here.

> driver). This driver provides intel_pmt_get_regions_by_feature()
> to list all available telemetry event aggregators. The list
> includes the "guid", the base address in MMIO space for the
> region where the event counters are exposed, and the package
> id where the CPUs that report to this aggregator are located.
> 
> Add a new Kconfig option CONFIG_X86_CPU_RESCTRL_INTEL_AET for the
> Intel specific parts of telemetry code. This depends on the
> INTEL_PMT_TELEMETRY and INTEL_TPMI drivers being built-in to the kernel
> for enumeration of telemetry features.
> 
> Call intel_pmt_get_regions_by_feature() for each pmt_feature_id
> that indicates per-RMID telemetry.
> 
> Save the returned pmt_feature_group pointers with guids that are known
> to resctrl for use at run time.
> 
> Those pointers will be returned to the INTEL_PMT_TELEMETRY subsystem at
> resctrl_arch_exit() time.

Last two paragraphs can merge.

intel_aet_exit() is empty here and I think that the code that "returns the
pointers" can actually be included here to make clear how the
"get" done in this patch is paired with a "put" to not make one wonder about
reference counting issues. I believe that doing so cleanly here (without the
active_event_groups that I find unnecessary ... more later) will make the code
more symmetrical and easier to follow while also removing the "just trust me
I'll do this later" uncertainty.

> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---

(missing the maintainer notes about checkpatch.pl troubles)

...

> diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> new file mode 100644
> index 000000000000..25075f369148
> --- /dev/null
> +++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> @@ -0,0 +1,120 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Resource Director Technology(RDT)
> + * - Intel Application Energy Telemetry
> + *
> + * Copyright (C) 2025 Intel Corporation
> + *
> + * Author:
> + *    Tony Luck <tony.luck@intel.com>
> + */
> +
> +#define pr_fmt(fmt)   "resctrl: " fmt
> +
> +#include <linux/cleanup.h>
> +#include <linux/cpu.h>
> +#include <linux/intel_vsec.h>
> +#include <linux/resctrl.h>
> +
> +#include "internal.h"
> +
> +/**
> + * struct event_group - All information about a group of telemetry events.
> + * @pfg:		Points to the aggregated telemetry space information
> + *			within the OOBMSM driver that contains data for all

"OOBMSM" -> "INTEL_PMT_TELEMETRY"?

> + *			telemetry regions.
> + * @guid:		Unique number per XML description file.
> + */
> +struct event_group {
> +	/* Data fields for additional structures to manage this group. */
> +	struct pmt_feature_group	*pfg;
> +
> +	/* Remaining fields initialized from XML file. */
> +	u32				guid;
> +};
> +
> +/*
> + * Link: https://github.com/intel/Intel-PMT
> + * File: xml/CWF/OOBMSM/RMID-ENERGY/cwf_aggregator.xml
> + */
> +static struct event_group energy_0x26696143 = {
> +	.guid		= 0x26696143,
> +};
> +
> +/*
> + * Link: https://github.com/intel/Intel-PMT
> + * File: xml/CWF/OOBMSM/RMID-PERF/cwf_aggregator.xml
> + */
> +static struct event_group perf_0x26557651 = {
> +	.guid		= 0x26557651,
> +};
> +
> +static struct event_group *known_energy_event_groups[] = {
> +	&energy_0x26696143,
> +};
> +
> +static struct event_group *known_perf_event_groups[] = {
> +	&perf_0x26557651,
> +};
> +
> +/* Stub for now */
> +static int discover_events(struct event_group *e, struct pmt_feature_group *p)
> +{
> +	return -EINVAL;
> +}
> +
> +DEFINE_FREE(intel_pmt_put_feature_group, struct pmt_feature_group *,
> +		if (!IS_ERR_OR_NULL(_T))
> +			intel_pmt_put_feature_group(_T))
> +
> +/*
> + * Make a request to the INTEL_PMT_DISCOVERY driver for the

"INTEL_PMT_DISCOVERY" -> "INTEL_PMT_TELEMETRY"

Please use line length available to not wrap lines so short.

> + * pmt_feature_group for a specific feature. If there is
> + * one the returned structure has an array of telemetry_region
> + * structures. Each describes one telemetry aggregator.
> + * Try to use every telemetry aggregator with a known guid.
> + */
> +static bool get_pmt_feature(enum pmt_feature_id feature, struct event_group **evgs,
> +			    unsigned int num_evg)
> +{
> +	struct pmt_feature_group *p __free(intel_pmt_put_feature_group) = NULL;
> +	struct event_group **peg;
> +	int ret;
> +
> +	p = intel_pmt_get_regions_by_feature(feature);
> +
> +	if (IS_ERR_OR_NULL(p))
> +		return false;
> +
> +	for (peg = evgs; peg < &evgs[num_evg]; peg++) {
> +		ret = discover_events(*peg, p);
> +		if (!ret) {
> +			(*peg)->pfg = no_free_ptr(p);
> +			return true;
> +		}
> +	}
> +
> +	return false;
> +}
> +
> +/*
> + * Ask OOBMSM discovery driver for all the RMID based telemetry groups

"OOBMSM discovery" -> "INTEL_PMT_TELEMETRY"

> + * that it supports.
> + */
> +bool intel_aet_get_events(void)
> +{
> +	bool ret1, ret2;
> +
> +	ret1 = get_pmt_feature(FEATURE_PER_RMID_ENERGY_TELEM,
> +			       known_energy_event_groups,
> +			       ARRAY_SIZE(known_energy_event_groups));
> +	ret2 = get_pmt_feature(FEATURE_PER_RMID_PERF_TELEM,
> +			       known_perf_event_groups,
> +			       ARRAY_SIZE(known_perf_event_groups));
> +
> +	return ret1 || ret2;
> +}
> +
> +void __exit intel_aet_exit(void)
> +{
> +}
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 58d890fe2100..56f0ff94c430 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -525,6 +525,19 @@ config X86_CPU_RESCTRL
>  
>  	  Say N if unsure.
>  
> +config X86_CPU_RESCTRL_INTEL_AET
> +	bool "Intel Application Energy Telemetry" if INTEL_PMT_TELEMETRY=y && INTEL_TPMI=y
> +	depends on X86_CPU_RESCTRL && CPU_SUP_INTEL
> +	help
> +	  Enable per-RMID telemetry events in resctrl

Missing period at end of sentence.

> +
> +	  Intel feature that collects per-RMID execution data
> +	  about energy consumption, measure of frequency independent
> +	  activity and other performance metrics. Data is aggregated
> +	  per package.
> +
> +	  Say N if unsure.
> +
>  config X86_FRED
>  	bool "Flexible Return and Event Delivery"
>  	depends on X86_64
> diff --git a/arch/x86/kernel/cpu/resctrl/Makefile b/arch/x86/kernel/cpu/resctrl/Makefile
> index d8a04b195da2..273ddfa30836 100644
> --- a/arch/x86/kernel/cpu/resctrl/Makefile
> +++ b/arch/x86/kernel/cpu/resctrl/Makefile
> @@ -1,6 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_X86_CPU_RESCTRL)		+= core.o rdtgroup.o monitor.o
>  obj-$(CONFIG_X86_CPU_RESCTRL)		+= ctrlmondata.o
> +obj-$(CONFIG_X86_CPU_RESCTRL_INTEL_AET)	+= intel_aet.o
>  obj-$(CONFIG_RESCTRL_FS_PSEUDO_LOCK)	+= pseudo_lock.o
>  
>  # To allow define_trace.h's recursive include:

Reinette