[PATCH V2 0/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[PATCH V2 0/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[Qinyun Tan]

V2:
- Keep sanity checks in the __mon_event_count to ensure execution occurs
  exclusively on CPUs sharing the same L3 cache cluster
- When reading the top level event, obtain a CPU within hdr.cpu_mask.
  Then use the cacheinfo shared_cpu_map of this CPU instead of using
  hdr.cpu_mask directly
- Adjust code formatting and commit log descriptions.

In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
structure previously relies on the cacheinfo interface to store L3 cache
information (e.g., shared_cpu_map) for monitoring. However, this approach
introduces risks when CPUs go offline:

The ci field in rdt_mon_domain 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) would fail, but returning zero
values for "top-level events" without error indication.

To resolve these issues:

1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).

2. The hdr.cpu_mask maintained by resctrl constitutes a subset of
shared_cpu_map. When reading top-level events, we dynamically select a CPU
from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl
to determine valid CPUs for reading RMID counter via the MSR interface.

Qinyun Tan (1):
  x86/resctrl: Remove unappropriate references to cacheinfo in the
    resctrl subsystem.

 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(-)

-- 
2.43.5

[PATCH V2 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[Qinyun Tan]

In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
structure previously relies on the cacheinfo interface to store L3 cache
information (e.g., shared_cpu_map) for monitoring. However, this approach
introduces risks when CPUs go offline:

The ci field in rdt_mon_domain 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) would fail, but returning zero
values for "top-level events" without error indication.

To resolve these issues:

1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).

2. The hdr.cpu_mask maintained by resctrl constitutes a subset of
shared_cpu_map. When reading top-level events, we dynamically select a CPU
from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl
to determine valid CPUs for reading RMID counter via the MSR interface.

Fixes: 328ea68874642 ("x86/resctrl: Prepare for new Sub-NUMA Cluster (SNC) monitor files")
Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.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;
-- 
2.43.5

Re: [PATCH V2 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[Reinette Chatre]

Hi Qinyun Tan,

Thank you very much. I have a few comments about the changelog that
I think will help explain the issue while aiming to have it follow the
"tip" rules documented in Documentation/process/maintainer-tip.rst. 

On 5/28/25 8:16 PM, Qinyun Tan wrote:
> In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
> structure previously relies on the cacheinfo interface to store L3 cache

"previously relies" -> "relies"

> information (e.g., shared_cpu_map) for monitoring. However, this approach
> introduces risks when CPUs go offline:
> 
> The ci field in rdt_mon_domain 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) would fail, but returning zero
> values for "top-level events" without error indication.

Last sentence of above paragraph can be modified slightly to keep it in
imperative tone:
	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.

> 
> To resolve these issues:

"To resolve these issues:" can be dropped. There is only one issue and the custom
is for the solution to follow the problem description.

> 
> 1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
> rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).
> 
> 2. The hdr.cpu_mask maintained by resctrl constitutes a subset of

"hdr.cpu_mask" -> "rdt_domain_hdr::cpu_mask"

I do not think "rdt_domain_hdr::cpu_mask" should be defined as a subset of
shared_cpu_map though ... especially since the problem description highlights how
shared_cpu_map can contain offline CPUs. How about:

"rdt_domain_hdr::cpu_mask contains the online CPUs associated with that
domain. When reading ..."

> shared_cpu_map. When reading top-level events, we dynamically select a CPU

drop "we" (no impersonating of code)

Considering the context it may help to be specific here:
"select a CPU" -> "select a (known to be online) CPU"

> from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl

"hdr.cpu_mask" -> "rdt_domain_hdr::cpu_mask"

> to determine valid CPUs for reading RMID counter via the MSR interface.

You can highlight the motivation for doing this. For example, "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."

Above is quite a mix of changes. Below aims to put it all together while also
adding more modifications as I am seeing the full picture. Please check for accuracy
and feel free to improve.

	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>
> ---

With changelog polished:
| Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Reinette

RE: [PATCH V2 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[Luck, Tony]

> To resolve these issues:
>
> 1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
> rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).
>
> 2. The hdr.cpu_mask maintained by resctrl constitutes a subset of
> shared_cpu_map. When reading top-level events, we dynamically select a CPU
> from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl
> to determine valid CPUs for reading RMID counter via the MSR interface.
>
> Fixes: 328ea68874642 ("x86/resctrl: Prepare for new Sub-NUMA Cluster (SNC) monitor files")
> Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>

Took this patch on a test run on a 2 socket Granite Rapids system configured
in SNC 3 mode.

While monitoring total memory bandwidth I took the first CPU on NUMA
nodes {1..5} offline. Monitoring kept working. Brought those back online.
Still OK. Took all CPUs on NUMA node 4 offline. Still good. Brought those
CPUs back online. Still good.

Tested-by: Tony Luck <tony.luck@intel.com>

-Tony

Re: [PATCH V2 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[qinyuntan]

Hi Tony Luck,

Thank you very much for your review and testing of my patch. Reinette 
has provided some suggestions based on the commit logs. After I modify 
the commit log, I will send you the third version of the patch.

Best regards,
Qinyun Tan

On 5/30/25 2:14 AM, Luck, Tony wrote:
>> To resolve these issues:
>>
>> 1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
>> rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).
>>
>> 2. The hdr.cpu_mask maintained by resctrl constitutes a subset of
>> shared_cpu_map. When reading top-level events, we dynamically select a CPU
>> from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl
>> to determine valid CPUs for reading RMID counter via the MSR interface.
>>
>> Fixes: 328ea68874642 ("x86/resctrl: Prepare for new Sub-NUMA Cluster (SNC) monitor files")
>> Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
> 
> Took this patch on a test run on a 2 socket Granite Rapids system configured
> in SNC 3 mode.
> 
> While monitoring total memory bandwidth I took the first CPU on NUMA
> nodes {1..5} offline. Monitoring kept working. Brought those back online.
> Still OK. Took all CPUs on NUMA node 4 offline. Still good. Brought those
> CPUs back online. Still good.
> 
> Tested-by: Tony Luck <tony.luck@intel.com>
> 
> -Tony

Re: [PATCH V2 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

[qinyuntan]

Hi Reinette Chatre,

Thank you very much for reviewing my patch and for correcting the commit 
log content. With your modifications, the commit log now looks much more 
reasonable.

I appreciate your patient guidance. I will resend the third version of 
the patch to you shortly.

Best regards,
Qinyun Tan

On 5/30/25 1:37 AM, Reinette Chatre wrote:
> Hi Qinyun Tan,
> 
> Thank you very much. I have a few comments about the changelog that
> I think will help explain the issue while aiming to have it follow the
> "tip" rules documented in Documentation/process/maintainer-tip.rst.
> 
> On 5/28/25 8:16 PM, Qinyun Tan wrote:
>> In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
>> structure previously relies on the cacheinfo interface to store L3 cache
> 
> "previously relies" -> "relies"
> 
>> information (e.g., shared_cpu_map) for monitoring. However, this approach
>> introduces risks when CPUs go offline:
>>
>> The ci field in rdt_mon_domain 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) would fail, but returning zero
>> values for "top-level events" without error indication.
> 
> Last sentence of above paragraph can be modified slightly to keep it in
> imperative tone:
> 	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.
> 
>>
>> To resolve these issues:
> 
> "To resolve these issues:" can be dropped. There is only one issue and the custom
> is for the solution to follow the problem description.
> 
>>
>> 1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
>> rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).
>>
>> 2. The hdr.cpu_mask maintained by resctrl constitutes a subset of
> 
> "hdr.cpu_mask" -> "rdt_domain_hdr::cpu_mask"
> 
> I do not think "rdt_domain_hdr::cpu_mask" should be defined as a subset of
> shared_cpu_map though ... especially since the problem description highlights how
> shared_cpu_map can contain offline CPUs. How about:
> 
> "rdt_domain_hdr::cpu_mask contains the online CPUs associated with that
> domain. When reading ..."
> 
>> shared_cpu_map. When reading top-level events, we dynamically select a CPU
> 
> drop "we" (no impersonating of code)
> 
> Considering the context it may help to be specific here:
> "select a CPU" -> "select a (known to be online) CPU"
> 
>> from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl
> 
> "hdr.cpu_mask" -> "rdt_domain_hdr::cpu_mask"
> 
>> to determine valid CPUs for reading RMID counter via the MSR interface.
> 
> You can highlight the motivation for doing this. For example, "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."
> 
> Above is quite a mix of changes. Below aims to put it all together while also
> adding more modifications as I am seeing the full picture. Please check for accuracy
> and feel free to improve.
> 
> 	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>
>> ---
> 
> With changelog polished:
> | Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> 
> Reinette