linux-kernel - [PATCH v13 09/27] x86/resctrl: Introduce interface to display number of free MBM counters

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Message-ID: <dc20bb6d3a654a3859f24fd036f4a095bd07c27f.1747349530.git.babu.moger@amd.com>
Date: Thu, 15 May 2025 17:51:54 -0500
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <tony.luck@...el.com>, <reinette.chatre@...el.com>,
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Subject: [PATCH v13 09/27] x86/resctrl: Introduce interface to display number of free MBM counters

Provide the interface to display the number of monitoring counters
available for assignment in each domain when mbm_cntr_assign mode is
enabled.

Signed-off-by: Babu Moger <babu.moger@....com>
---
v13: Resolved conflicts caused by the recent FS/ARCH code restructure.
     The files monitor.c and rdtgroup.c file has now been split between
     the FS and ARCH directories.

v12: Minor change to change log.
     Updated the documentation text with an example.
     Replaced seq_puts(s, ";") with seq_putc(s, ';');
     Added missing rdt_last_cmd_clear() in resctrl_available_mbm_cntrs_show().

v11: Rename rdtgroup_available_mbm_cntrs_show() to resctrl_available_mbm_cntrs_show().
     Few minor text changes.

v10: Patch changed to handle the counters at domain level.
     https://lore.kernel.org/lkml/CALPaoCj+zWq1vkHVbXYP0znJbe6Ke3PXPWjtri5AFgD9cQDCUg@mail.gmail.com/
     So, display logic also changed now.

v9: New patch
---
 Documentation/filesystems/resctrl.rst | 11 ++++++
 fs/resctrl/monitor.c                  |  5 ++-
 fs/resctrl/rdtgroup.c                 | 48 +++++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index abbbbdf61062..2bfad43aac9c 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -295,6 +295,17 @@ with the following files:
 	  # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
 	  0=32;1=32
 
+"available_mbm_cntrs":
+	The number of monitoring counters available for assignment in each
+	domain when mbm_cntr_assign mode is enabled on the system.
+
+	For example, on a system with 30 available [hardware] monitoring counters
+	in each of its L3 domains:
+	::
+
+	  # cat /sys/fs/resctrl/info/L3_MON/available_mbm_cntrs
+	  0=30;1=30
+
 "max_threshold_occupancy":
 		Read/write file provides the largest value (in
 		bytes) at which a previously used LLC_occupancy
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 039516cf410d..2548aee0151c 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -918,9 +918,12 @@ int resctrl_mon_resource_init(void)
 	else if (resctrl_arch_is_mbm_total_enabled())
 		mba_mbps_default_event = QOS_L3_MBM_TOTAL_EVENT_ID;
 
-	if (r->mon.mbm_cntr_assignable)
+	if (r->mon.mbm_cntr_assignable) {
 		resctrl_file_fflags_init("num_mbm_cntrs",
 					 RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
+		resctrl_file_fflags_init("available_mbm_cntrs",
+					 RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
+	}
 
 	return 0;
 }
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index e2005fc9acd9..752750e3e443 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1855,6 +1855,48 @@ static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+static int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
+					    struct seq_file *s, void *v)
+{
+	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
+	struct rdt_mon_domain *dom;
+	bool sep = false;
+	u32 cntrs, i;
+	int ret = 0;
+
+	cpus_read_lock();
+	mutex_lock(&rdtgroup_mutex);
+
+	rdt_last_cmd_clear();
+
+	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		rdt_last_cmd_puts("mbm_cntr_assign mode is not enabled\n");
+		ret = -EINVAL;
+		goto unlock_cntrs_show;
+	}
+
+	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
+		if (sep)
+			seq_putc(s, ';');
+
+		cntrs = 0;
+		for (i = 0; i < r->mon.num_mbm_cntrs; i++) {
+			if (!dom->cntr_cfg[i].rdtgrp)
+				cntrs++;
+		}
+
+		seq_printf(s, "%d=%u", dom->hdr.id, cntrs);
+		sep = true;
+	}
+	seq_putc(s, '\n');
+
+unlock_cntrs_show:
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	return ret;
+}
+
 /* rdtgroup information files for one cache resource. */
 static struct rftype res_common_files[] = {
 	{
@@ -1878,6 +1920,12 @@ static struct rftype res_common_files[] = {
 		.seq_show	= rdt_mon_features_show,
 		.fflags		= RFTYPE_MON_INFO,
 	},
+	{
+		.name		= "available_mbm_cntrs",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= resctrl_available_mbm_cntrs_show,
+	},
 	{
 		.name		= "num_rmids",
 		.mode		= 0444,
-- 
2.34.1