linux-kernel - Re: [PATCH v19 08/20] x86/resctrl: Prepare for new Sub-NUMA Cluster (SNC) monitor files

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Date: Thu, 30 May 2024 13:21:01 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.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>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v19 08/20] x86/resctrl: Prepare for new Sub-NUMA Cluster
 (SNC) monitor files

Hi Tony,

On 5/28/24 3:19 PM, Tony Luck wrote:
> When SNC is enabled monitoring data is collected at the SNC node
> granularity, but must be reported at L3-cache granularity for
> backwards compatibility in addition to reporting at the node
> level.
> 
> Add a "ci" field to the rdt_mon_domain structure to save the
> cache information about the enclosing L3 cache for the domain.
> This provides:
> 
> 1) The cache id which is needed to compose the name of the legacy
> monitoring directory, and to determine which domains should be
> summed to provide L3-scoped data.
> 
> 2) The shared_cpu_map which is needed to determine which CPUs can
> be used to read the RMID counters with the MSR interface.
> 
> This is the first step to an eventual goal of monitor reporting files
> like this (for a system with two SNC nodes per L3):
> 
> $ cd /sys/fs/resctrl/mon_data
> $ tree mon_L3_00
> mon_L3_00			<- 00 here is L3 cache id
> ├── llc_occupancy		\  These files provide legacy support
> ├── mbm_local_bytes		 > for non-SNC aware monitor apps
> ├── mbm_total_bytes		/  that expect data at L3 cache level
> ├── mon_sub_L3_00		<- 00 here is SNC node id
> │   ├── llc_occupancy		\  These files are finer grained
> │   ├── mbm_local_bytes		 > data from each SNC node
> │   └── mbm_total_bytes		/
> └── mon_sub_L3_01
>      ├── llc_occupancy		\
>      ├── mbm_local_bytes		 > As above, but for node 1.
>      └── mbm_total_bytes		/
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>   include/linux/resctrl.h                   |  2 ++
>   arch/x86/kernel/cpu/resctrl/internal.h    | 21 +++++++++++++++++++++
>   arch/x86/kernel/cpu/resctrl/core.c        |  7 ++++++-
>   arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  1 -
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c    |  1 -
>   5 files changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 64b6ad1b22a1..d733e1f6485d 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -96,6 +96,7 @@ struct rdt_ctrl_domain {
>   /**
>    * struct rdt_mon_domain - group of CPUs sharing a resctrl monitor resource
>    * @hdr:		common header for different domain types
> + * @ci:			cache info for this domain
>    * @rmid_busy_llc:	bitmap of which limbo RMIDs are above threshold
>    * @mbm_total:		saved state for MBM total bandwidth
>    * @mbm_local:		saved state for MBM local bandwidth
> @@ -106,6 +107,7 @@ struct rdt_ctrl_domain {
>    */
>   struct rdt_mon_domain {
>   	struct rdt_domain_hdr		hdr;
> +	struct cacheinfo		*ci;
>   	unsigned long			*rmid_busy_llc;
>   	struct mbm_state		*mbm_total;
>   	struct mbm_state		*mbm_local;
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 135190e0711c..eb70d3136ced 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -2,6 +2,7 @@
>   #ifndef _ASM_X86_RESCTRL_INTERNAL_H
>   #define _ASM_X86_RESCTRL_INTERNAL_H
>   
> +#include <linux/cacheinfo.h>
>   #include <linux/resctrl.h>
>   #include <linux/sched.h>
>   #include <linux/kernfs.h>
> @@ -509,6 +510,26 @@ static inline bool resctrl_arch_get_cdp_enabled(enum resctrl_res_level l)
>   
>   int resctrl_arch_set_cdp_enabled(enum resctrl_res_level l, bool enable);
>   
> +/*
> + * Get the cacheinfo structure of the cache associated with @cpu at level @level.
> + * cpuhp lock must be held.
> + */
> +static inline struct cacheinfo *get_cpu_cacheinfo_level(int cpu, int level)
> +{
> +	struct cpu_cacheinfo *ci = get_cpu_cacheinfo(cpu);
> +	int i;
> +
> +	for (i = 0; i < ci->num_leaves; i++) {
> +		if (ci->info_list[i].level == level) {
> +			if (ci->info_list[i].attributes & CACHE_ID)
> +				return &ci->info_list[i];
> +			break;
> +		}
> +	}
> +
> +	return NULL;
> +}
> +

This does not belong in resctrl. It really looks to partner well with existing
cache helpers in include/linux/cacheinfo.h that already contains get_cpu_cacheinfo_id().
Considering the existing naming get_cpu_cacheinfo() may be more appropriate.

Reinette