linux-kernel - Re: [PATCH v7 28/31] x86/resctrl: Enable RDT_RESOURCE_PERF

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Message-ID: <75e37257-49b7-443b-a409-885811d04dd0@intel.com>
Date: Fri, 25 Jul 2025 16:54:50 -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 v7 28/31] x86/resctrl: Enable RDT_RESOURCE_PERF_PKG

Hi Tony,

On 7/11/25 4:53 PM, Tony Luck wrote:
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 1a6635cc5b37..1d07c38ed528 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -774,14 +774,26 @@ static int resctrl_arch_offline_cpu(unsigned int cpu)
>  
>  void resctrl_arch_pre_mount(void)
>  {
> +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_PERF_PKG].r_resctrl;
>  	static atomic_t only_once = ATOMIC_INIT(0);
> -	int old = 0;
> +	int cpu, old = 0;
>  
>  	if (!atomic_try_cmpxchg(&only_once, &old, 1))
>  		return;
>  
>  	if (!intel_aet_get_events())
>  		return;
> +
> +	/*
> +	 * Late discovery of telemetry events means the domains for the
> +	 * resource were not built. Do that now.
> +	 */
> +	cpus_read_lock();
> +	mutex_lock(&domain_list_lock);
> +	for_each_online_cpu(cpu)
> +		domain_add_cpu_mon(cpu, r);

Without an explicit "mon_capable" check this change now creates a new "contract" that
"if intel_aet_get_events() succeeds then PERF_PKG is mon_capable". I do not believe this
additional complication justifies saving a line of code.

> +	mutex_unlock(&domain_list_lock);
> +	cpus_read_unlock();
>  }
>  
>  enum {
> diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> index 6958efbf7e81..ea7a782c1661 100644
> --- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
> +++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> @@ -264,6 +264,9 @@ static int discover_events(struct event_group *e, struct pmt_feature_group *p)
>  	else
>  		r->num_rmid = e->num_rmids;
>  
> +	pr_info("%s %s monitoring detected\n", r->name, e->name);
> +	r->mon_capable = true;
> +
>  	return 0;
>  }
>  

Reinette