linux-kernel - Re: [PATCH v3 07/26] x86/resctrl: Move L3 initialization out of domain_add_cpu

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Message-ID: <698ab022-b6c1-4fca-b42d-26a3b4b2b8e8@intel.com>
Date: Fri, 18 Apr 2025 14:51:01 -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>, Anil Keshavamurthy <anil.s.keshavamurthy@...el.com>
CC: <linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v3 07/26] x86/resctrl: Move L3 initialization out of
 domain_add_cpu_mon()

Hi Tony,

On 4/7/25 4:40 PM, Tony Luck wrote:
> To prepare for additional types of monitoring domains, move all the
> L3 specific initialization into a helper function.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/kernel/cpu/resctrl/core.c | 57 ++++++++++++++++++------------
>  1 file changed, 35 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index d82a4a2db699..703423b0be0e 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -493,33 +493,12 @@ static void domain_add_cpu_ctrl(int cpu, struct rdt_resource *r)
>  	}
>  }
>  
> -static void domain_add_cpu_mon(int cpu, struct rdt_resource *r)
> +static void setup_l3_mon_domain(int cpu, int id, struct rdt_resource *r, struct list_head *add_pos)
>  {
> -	int id = get_domain_id_from_scope(cpu, r->mon_scope);
> -	struct list_head *add_pos = NULL;
>  	struct rdt_hw_mon_domain *hw_dom;
> -	struct rdt_domain_hdr *hdr;
>  	struct rdt_mon_domain *d;
>  	int err;
>  
> -	lockdep_assert_held(&domain_list_lock);
> -
> -	if (id < 0) {
> -		pr_warn_once("Can't find monitor domain id for CPU:%d scope:%d for resource %s\n",
> -			     cpu, r->mon_scope, r->name);
> -		return;
> -	}
> -
> -	hdr = resctrl_find_domain(&r->mon_domains, id, &add_pos);
> -	if (hdr) {
> -		if (WARN_ON_ONCE(hdr->type != DOMTYPE(r->rid, DOMTYPE_MON)))
> -			return;
> -		d = container_of(hdr, struct rdt_mon_domain, hdr);
> -
> -		cpumask_set_cpu(cpu, &d->hdr.cpu_mask);
> -		return;
> -	}
> -

Many functions called by this new "setup_l3_mon_domain()" are specific to L3 resource but
since L3 resource has so far been the only one supported the naming has been generic. Now that
this function is made resource specific I think it will help make the code clear if the
L3 specific functions called by it are also renamed. For example, mon_domain_free() can
be renamed to free_l3_mon_domain() to match the "setup_l3_mon_domain()" introduced here. Also
arch_mon_domain_online() -> arch_l3_mon_domain_online().
Seems like resctrl_online_mon_domain() is only temporarily specific to L3 in this series
(would be helpful if such details are explained in changelog) ... to start it could
include a check that ensures it is only called on L3 resource and then it will help
to clarify what this patch does and how following work builds on it.

>  	hw_dom = kzalloc_node(sizeof(*hw_dom), GFP_KERNEL, cpu_to_node(cpu));
>  	if (!hw_dom)
>  		return;
> @@ -552,6 +531,40 @@ static void domain_add_cpu_mon(int cpu, struct rdt_resource *r)
>  	}
>  }
>  
Reinette