Message-ID: <4e275fadf59e36e38ac60406a19cdf67d640f7d2.1752167718.git.babu.moger@amd.com>
Date: Thu, 10 Jul 2025 12:16:20 -0500
From: Babu Moger <babu.moger@....com>
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Subject: [PATCH v7 06/10] fs/resctrl: Introduce interface to display "io_alloc" support

"io_alloc" feature in resctrl allows direct insertion of data from I/O
devices into the cache.

Introduce the 'io_alloc' resctrl file to indicate the support for the
feature.

Signed-off-by: Babu Moger <babu.moger@....com>
---
v7: Updated the changelog.
    Updated user doc for io_alloc in resctrl.rst.
    Added mutex rdtgroup_mutex in resctrl_io_alloc_show();

v6: Added "io_alloc_cbm" details in user doc resctrl.rst.
    Resource name is not printed in CBM now. Corrected the texts about it
    in resctrl.rst.

v5: Resolved conflicts due to recent resctrl FS/ARCH code restructure.
    Updated show_doms() to print the resource if only it is valid. Pass NULL while
    printing io_alloc CBM.
    Changed the code to access the CBMs via either L3CODE or L3DATA resources.

v4: Updated the change log.
    Added rdtgroup_mutex before rdt_last_cmd_puts().
    Returned -ENODEV when resource type is CDP_DATA.
    Kept the resource name while printing the CBM (L3:0=fff) that way
    I dont have to change show_doms() just for this feature and it is
    consistant across all the schemata display.

v3: Minor changes due to changes in resctrl_arch_get_io_alloc_enabled()
    and resctrl_io_alloc_closid_get().
    Added the check to verify CDP resource type.
    Updated the commit log.

v2: Fixed to display only on L3 resources.
    Added the locks while processing.
    Rename the displat to io_alloc_cbm (from sdciae_cmd).
---
 Documentation/filesystems/resctrl.rst | 25 +++++++++++++++++
 fs/resctrl/rdtgroup.c                 | 39 +++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index c3c412733632..354e6a00fa45 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -143,6 +143,31 @@ related to allocation:
 			"1":
 			      Non-contiguous 1s value in CBM is supported.
 
+"io_alloc":
+		"io_alloc" enables system software to configure the portion of
+		the cache allocated for I/O traffic. File may only exist if the
+		system supports this feature on some of its cache resources.
+
+			"disabled":
+			      Portions of cache used for allocation of I/O traffic
+			      cannot be configured.
+			"enabled":
+			      Portions of cache used for allocation of I/O traffic
+			      can be configured using "io_alloc_cbm".
+			"not supported":
+			      Support not available on the system.
+
+		The underlying implementation may reduce resources available to
+		general (CPU) cache allocation. See architecture specific notes
+		below. Depending on usage requirements the feature can be enabled
+		or disabled:
+
+		On AMD systems, the io_alloc feature is supported by the L3 Smart
+		Data Cache Injection Allocation Enforcement (SDCIAE). The CLOSID for
+		io_alloc is determined by the highest CLOSID supported by the resource.
+		When CDP is enabled, io_alloc routes I/O traffic using the highest
+		CLOSID allocated for the instruction cache (L3CODE).
+
 Memory bandwidth(MB) subdirectory contains the following files
 with respect to allocation:
 
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index a2eea85aecc8..d7c4417b4516 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1836,6 +1836,28 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
 	return ret ?: nbytes;
 }
 
+static int resctrl_io_alloc_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;
+
+	mutex_lock(&rdtgroup_mutex);
+
+	if (r->cache.io_alloc_capable) {
+		if (resctrl_arch_get_io_alloc_enabled(r))
+			seq_puts(seq, "enabled\n");
+		else
+			seq_puts(seq, "disabled\n");
+	} else {
+		seq_puts(seq, "not supported\n");
+	}
+
+	mutex_unlock(&rdtgroup_mutex);
+
+	return 0;
+}
+
 /* rdtgroup information files for one cache resource. */
 static struct rftype res_common_files[] = {
 	{
@@ -1926,6 +1948,12 @@ static struct rftype res_common_files[] = {
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= rdt_thread_throttle_mode_show,
 	},
+	{
+		.name		= "io_alloc",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= resctrl_io_alloc_show,
+	},
 	{
 		.name		= "max_threshold_occupancy",
 		.mode		= 0644,
@@ -2095,6 +2123,15 @@ static void thread_throttle_mode_init(void)
 				 RFTYPE_CTRL_INFO | RFTYPE_RES_MB);
 }
 
+static void io_alloc_init(void)
+{
+	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
+
+	if (r->cache.io_alloc_capable)
+		resctrl_file_fflags_init("io_alloc", RFTYPE_CTRL_INFO |
+					 RFTYPE_RES_CACHE);
+}
+
 void resctrl_file_fflags_init(const char *config, unsigned long fflags)
 {
 	struct rftype *rft;
@@ -4282,6 +4319,8 @@ int resctrl_init(void)
 
 	thread_throttle_mode_init();
 
+	io_alloc_init();
+
 	ret = resctrl_mon_resource_init();
 	if (ret)
 		return ret;
-- 
2.34.1

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