linux-kernel - [RFC PATCH 03/19] fs/resctrl: Add new interface max

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Message-ID: <a4ca7d43100132b79adba85a4674c7b46b05bb8c.1769029977.git.babu.moger@amd.com>
Date: Wed, 21 Jan 2026 15:12:41 -0600
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <tony.luck@...el.com>, <reinette.chatre@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <babu.moger@....com>,
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Subject: [RFC PATCH 03/19] fs/resctrl: Add new interface max_bandwidth

While min_bandwidth is exposed for each resource under
/sys/fs/resctrl, the maximum supported bandwidth is not currently shown.

Add max_bandwidth to report the maximum bandwidth permitted for a resource.
This helps users understand the limits of the associated resource control
group.

Signed-off-by: Babu Moger <babu.moger@....com>
---
 Documentation/filesystems/resctrl.rst |  6 +++++-
 fs/resctrl/rdtgroup.c                 | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 45dde8774128..94187dd3c244 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -224,7 +224,11 @@ Memory bandwidth(MB) subdirectory contains the following files
 with respect to allocation:
 
 "min_bandwidth":
-		The minimum memory bandwidth percentage which
+		The minimum memory bandwidth percentage or units which
+		user can request.
+
+"max_bandwidth":
+		The maximum memory bandwidth percentage or units which
 		user can request.
 
 "bandwidth_gran":
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index ae6c515f4c19..d2eab9007cc1 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1153,6 +1153,16 @@ static int rdt_min_bw_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+static int rdt_max_bw_show(struct kernfs_open_file *of,
+			   struct seq_file *seq, void *v)
+{
+	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
+	struct rdt_resource *r = s->res;
+
+	seq_printf(seq, "%u\n", r->membw.max_bw);
+	return 0;
+}
+
 static int rdt_num_rmids_show(struct kernfs_open_file *of,
 			      struct seq_file *seq, void *v)
 {
@@ -1959,6 +1969,13 @@ static struct rftype res_common_files[] = {
 		.seq_show	= rdt_min_bw_show,
 		.fflags		= RFTYPE_CTRL_INFO | RFTYPE_RES_MB,
 	},
+	{
+		.name		= "max_bandwidth",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdt_max_bw_show,
+		.fflags		= RFTYPE_CTRL_INFO | RFTYPE_RES_MB,
+	},
 	{
 		.name		= "bandwidth_gran",
 		.mode		= 0444,
-- 
2.34.1