linux-kernel - Re: [PATCH v12 19/31] x86/resctrl: Read telemetry events

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Message-ID: <a8ee6c4e-7390-4313-9b34-6133186d2f7a@intel.com>
Date: Wed, 22 Oct 2025 21:47:51 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghuay@...dia.com>, "Maciej
 Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>, Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v12 19/31] x86/resctrl: Read telemetry events

Hi Tony,

On 10/13/25 3:33 PM, Tony Luck wrote:
> Telemetry events are enabled during the first mount of the resctrl
> file system.

Not clear how above is relevant to this patch?

> 
> Mark telemetry regions that did not pass the sanity checks by
> clearing their MMIO address fields so that they will not be
> used when reading events.

Above is definitely not relevant.

> 
> Introduce intel_aet_read_event() to read telemetry events for resource
> RDT_RESOURCE_PERF_PKG. There may be multiple aggregators tracking each
> package, so scan all of them and add up all counters. Aggregators may
> return an invalid data indication if they have received no records for
> a given RMID. Return success to the user if one or more aggregators
> provide valid data.

"success" (via return code of 0) is always returned to the user. The
difference is whether user will see event data, "Unavailable", or "Error".

> 
> Resctrl now uses readq() so depends on X86_64. Update Kconfig.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---

...

> @@ -230,3 +234,47 @@ void __exit intel_aet_exit(void)
>  		(*peg)->pfg = NULL;
>  	}
>  }
> +
> +#define DATA_VALID	BIT_ULL(63)
> +#define DATA_BITS	GENMASK_ULL(62, 0)
> +
> +/*
> + * Read counter for an event on a domain (summing all aggregators
> + * on the domain). If an aggregator hasn't received any data for a
> + * specific RMID, the MMIO read indicates that data is not valid.
> + * Return success if at least one aggregator has valid data.
> + */
> +int intel_aet_read_event(int domid, u32 rmid, enum resctrl_event_id eventid,
> +			 void *arch_priv, u64 *val)
> +{
> +	struct pmt_event *pevt = arch_priv;
> +	struct event_group *e;
> +	bool valid = false;
> +	u64 evtcount;
> +	void *pevt0;
> +	u32 idx;
> +
> +	pevt0 = pevt - pevt->idx;
> +	e = container_of(pevt0, struct event_group, evts);
> +	idx = rmid * e->num_events;
> +	idx += pevt->idx;
> +
> +	if (idx * sizeof(u64) + sizeof(u64) > e->mmio_size) {
> +		pr_warn_once("MMIO index %u out of range\n", idx);
> +		return -EIO;
> +	}
> +
> +	for (int i = 0; i < e->pfg->count; i++) {
> +		if (!e->pfg->regions[i].addr)
> +			continue;
> +		if (e->pfg->regions[i].plat_info.package_id != domid)
> +			continue;
> +		evtcount = readq(e->pfg->regions[i].addr + idx * sizeof(u64));
> +		if (!(evtcount & DATA_VALID))
> +			continue;
> +		*val += evtcount & DATA_BITS;

I missed this before. This just blindly adds the event data to whichever variable the
caller provides. Could you please instead use a local variable to do this addition and
on success assign it to the provided val parameter?

> +		valid = true;
> +	}
> +
> +	return valid ? 0 : -EINVAL;
> +}
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 5565a8752266..6804b83934e8 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -252,6 +252,9 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain_hdr *hdr,
>  
>  	resctrl_arch_rmid_read_context_check();
>  
> +	if (r->rid == RDT_RESOURCE_PERF_PKG)
> +		return intel_aet_read_event(hdr->id, rmid, eventid, arch_priv, val);
> +
>  	if (!domain_header_is_valid(hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3))
>  		return -EINVAL;
>  
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index faaa2851c5c2..84a0cbe90748 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -526,12 +526,26 @@ static bool cpu_on_correct_domain(struct rmid_read *rr)
>  
>  static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>  {
> +	u64 tval = 0;

please declare this variable local to the PERF_PKG block to help keep the
different resource code separate.

> +
>  	if (!cpu_on_correct_domain(rr))
>  		return -EINVAL;
>  
>  	switch (rr->r->rid) {
>  	case RDT_RESOURCE_L3:
>  		return __l3_mon_event_count(rdtgrp, rr);
> +
> +	case RDT_RESOURCE_PERF_PKG:
> +		rr->err = resctrl_arch_rmid_read(rr->r, rr->hdr, rdtgrp->closid,
> +						 rdtgrp->mon.rmid, rr->evt->evtid,
> +						 rr->evt->arch_priv,
> +						 &tval, rr->arch_mon_ctx);
> +		if (rr->err)
> +			return rr->err;
> +
> +		rr->val += tval;
> +
> +		return 0;
>  	default:
>  		return -EINVAL;
>  	}

Reinette