Re: [PATCH V4 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

["Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>]

Hi Qinyun,

Ever since this resctrl subsystem has been refactored to support other 
architectures by moving common files related to filesystem handling into 
fs/resctrl/*, I have seen folks started to tag the subject line with 
"x86,fs/resctrl:" when patch touches files under fs/resctrl. Since your 
patches touches files under both arch/x86 and fs/resctrl/*, can you 
please accommodate this subject tag -> "x86,fs/resctrl:" so we are 
consistent.

/Anil

On 5/30/2025 10:50 AM, Qinyun Tan wrote:
> In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
> structure representing a NUMA node relies on the cacheinfo interface
> (rdt_mon_domain::ci) to store L3 cache information (e.g., shared_cpu_map)
> for monitoring. The L3 cache information of a SNC NUMA node determines
> which domains are summed for the "top level" L3-scoped events.
>
> rdt_mon_domain::ci is initialized using the first online CPU of a NUMA
> node. When this CPU goes offline, its shared_cpu_map is cleared to contain
> only the offline CPU itself. Subsequently, attempting to read counters
> via smp_call_on_cpu(offline_cpu) fails (and error ignored), returning
> zero values for "top-level events" without any error indication. Replace
> the cacheinfo references in struct rdt_mon_domain and struct rmid_read
> with the cacheinfo ID (a unique identifier for the L3 cache).
>
> rdt_domain_hdr::cpu_mask contains the online CPUs associated with that
> domain. When reading "top-level events", select a CPU from
> rdt_domain_hdr::cpu_mask and utilize its L3 shared_cpu_map to determine
> valid CPUs for reading RMID counter via the MSR interface.
>
> Considering all CPUs associated with the L3 cache improves the chances
> of picking a housekeeping CPU on which the counter reading work can be
> queued, avoiding an unnecessary IPI.
>
> Fixes: 328ea68874642 ("x86/resctrl: Prepare for new Sub-NUMA Cluster (SNC) monitor files")
> Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
> Tested-by: Tony Luck <tony.luck@intel.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
>   arch/x86/kernel/cpu/resctrl/core.c |  6 ++++--
>   fs/resctrl/ctrlmondata.c           | 13 +++++++++----
>   fs/resctrl/internal.h              |  4 ++--
>   fs/resctrl/monitor.c               |  6 ++++--
>   fs/resctrl/rdtgroup.c              |  6 +++---
>   include/linux/resctrl.h            |  4 ++--
>   6 files changed, 24 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 7109cbfcad4fd..187d527ef73b6 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -498,6 +498,7 @@ static void domain_add_cpu_mon(int cpu, struct rdt_resource *r)
>   	struct rdt_hw_mon_domain *hw_dom;
>   	struct rdt_domain_hdr *hdr;
>   	struct rdt_mon_domain *d;
> +	struct cacheinfo *ci;
>   	int err;
>   
>   	lockdep_assert_held(&domain_list_lock);
> @@ -525,12 +526,13 @@ static void domain_add_cpu_mon(int cpu, struct rdt_resource *r)
>   	d = &hw_dom->d_resctrl;
>   	d->hdr.id = id;
>   	d->hdr.type = RESCTRL_MON_DOMAIN;
> -	d->ci = get_cpu_cacheinfo_level(cpu, RESCTRL_L3_CACHE);
> -	if (!d->ci) {
> +	ci = get_cpu_cacheinfo_level(cpu, RESCTRL_L3_CACHE);
> +	if (!ci) {
>   		pr_warn_once("Can't find L3 cache for CPU:%d resource %s\n", cpu, r->name);
>   		mon_domain_free(hw_dom);
>   		return;
>   	}
> +	d->ci_id = ci->id;
>   	cpumask_set_cpu(cpu, &d->hdr.cpu_mask);
>   
>   	arch_mon_domain_online(r, d);
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index 6ed2dfd4dbbd9..d98e0d2de09fd 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -594,9 +594,10 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>   	struct rmid_read rr = {0};
>   	struct rdt_mon_domain *d;
>   	struct rdtgroup *rdtgrp;
> +	int domid, cpu, ret = 0;
>   	struct rdt_resource *r;
> +	struct cacheinfo *ci;
>   	struct mon_data *md;
> -	int domid, ret = 0;
>   
>   	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>   	if (!rdtgrp) {
> @@ -623,10 +624,14 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>   		 * one that matches this cache id.
>   		 */
>   		list_for_each_entry(d, &r->mon_domains, hdr.list) {
> -			if (d->ci->id == domid) {
> -				rr.ci = d->ci;
> +			if (d->ci_id == domid) {
> +				rr.ci_id = d->ci_id;
> +				cpu = cpumask_any(&d->hdr.cpu_mask);
> +				ci = get_cpu_cacheinfo_level(cpu, RESCTRL_L3_CACHE);
> +				if (!ci)
> +					continue;
>   				mon_event_read(&rr, r, NULL, rdtgrp,
> -					       &d->ci->shared_cpu_map, evtid, false);
> +					       &ci->shared_cpu_map, evtid, false);
>   				goto checkresult;
>   			}
>   		}
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index 9a8cf6f11151d..0a1eedba2b03a 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -98,7 +98,7 @@ struct mon_data {
>    *	   domains in @r sharing L3 @ci.id
>    * @evtid: Which monitor event to read.
>    * @first: Initialize MBM counter when true.
> - * @ci:    Cacheinfo for L3. Only set when @d is NULL. Used when summing domains.
> + * @ci_id: Cacheinfo id for L3. Only set when @d is NULL. Used when summing domains.
>    * @err:   Error encountered when reading counter.
>    * @val:   Returned value of event counter. If @rgrp is a parent resource group,
>    *	   @val includes the sum of event counts from its child resource groups.
> @@ -112,7 +112,7 @@ struct rmid_read {
>   	struct rdt_mon_domain	*d;
>   	enum resctrl_event_id	evtid;
>   	bool			first;
> -	struct cacheinfo	*ci;
> +	unsigned int		ci_id;
>   	int			err;
>   	u64			val;
>   	void			*arch_mon_ctx;
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index bde2801289d35..f5637855c3aca 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -361,6 +361,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
>   {
>   	int cpu = smp_processor_id();
>   	struct rdt_mon_domain *d;
> +	struct cacheinfo *ci;
>   	struct mbm_state *m;
>   	int err, ret;
>   	u64 tval = 0;
> @@ -388,7 +389,8 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
>   	}
>   
>   	/* Summing domains that share a cache, must be on a CPU for that cache. */
> -	if (!cpumask_test_cpu(cpu, &rr->ci->shared_cpu_map))
> +	ci = get_cpu_cacheinfo_level(cpu, RESCTRL_L3_CACHE);
> +	if (!ci || ci->id != rr->ci_id)
>   		return -EINVAL;
>   
>   	/*
> @@ -400,7 +402,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
>   	 */
>   	ret = -EINVAL;
>   	list_for_each_entry(d, &rr->r->mon_domains, hdr.list) {
> -		if (d->ci->id != rr->ci->id)
> +		if (d->ci_id != rr->ci_id)
>   			continue;
>   		err = resctrl_arch_rmid_read(rr->r, d, closid, rmid,
>   					     rr->evtid, &tval, rr->arch_mon_ctx);
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index cc37f58b47dd7..74b25bbb9872c 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -3034,7 +3034,7 @@ static void rmdir_mondata_subdir_allrdtgrp(struct rdt_resource *r,
>   	char name[32];
>   
>   	snc_mode = r->mon_scope == RESCTRL_L3_NODE;
> -	sprintf(name, "mon_%s_%02d", r->name, snc_mode ? d->ci->id : d->hdr.id);
> +	sprintf(name, "mon_%s_%02d", r->name, snc_mode ? d->ci_id : d->hdr.id);
>   	if (snc_mode)
>   		sprintf(subname, "mon_sub_%s_%02d", r->name, d->hdr.id);
>   
> @@ -3059,7 +3059,7 @@ static int mon_add_all_files(struct kernfs_node *kn, struct rdt_mon_domain *d,
>   		return -EPERM;
>   
>   	list_for_each_entry(mevt, &r->evt_list, list) {
> -		domid = do_sum ? d->ci->id : d->hdr.id;
> +		domid = do_sum ? d->ci_id : d->hdr.id;
>   		priv = mon_get_kn_priv(r->rid, domid, mevt, do_sum);
>   		if (WARN_ON_ONCE(!priv))
>   			return -EINVAL;
> @@ -3087,7 +3087,7 @@ static int mkdir_mondata_subdir(struct kernfs_node *parent_kn,
>   	lockdep_assert_held(&rdtgroup_mutex);
>   
>   	snc_mode = r->mon_scope == RESCTRL_L3_NODE;
> -	sprintf(name, "mon_%s_%02d", r->name, snc_mode ? d->ci->id : d->hdr.id);
> +	sprintf(name, "mon_%s_%02d", r->name, snc_mode ? d->ci_id : d->hdr.id);
>   	kn = kernfs_find_and_get(parent_kn, name);
>   	if (kn) {
>   		/*
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 9ba771f2ddead..6fb4894b8cfd1 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -159,7 +159,7 @@ 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
> + * @ci_id:		cache info id 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
> @@ -170,7 +170,7 @@ struct rdt_ctrl_domain {
>    */
>   struct rdt_mon_domain {
>   	struct rdt_domain_hdr		hdr;
> -	struct cacheinfo		*ci;
> +	unsigned int			ci_id;
>   	unsigned long			*rmid_busy_llc;
>   	struct mbm_state		*mbm_total;
>   	struct mbm_state		*mbm_local;