alinux: introduce psi_v1 boot parameter

Instead using static kconfig CONFIG_PSI_CGROUP_V1, we introduce a boot
parameter psi_v1 to enable psi cgroup v1 support. Default it is
disabled, which means when passing psi=1 boot parameter, we only support
cgroup v2.
This is to keep consistent with other cgroup v1 features such as cgroup
writeback v1 (cgwb_v1).
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXunlei Pang <xlpang@linux.alibaba.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -3598,6 +3598,10 @@
 			tracking.
 			Format: <bool>
 
+	psi_v1=		[KNL] Enable or disable pressure stall information
+			tracking on cgroup v1.
+			Format: <bool>
+
 	psmouse.proto=	[HW,MOUSE] Highest PS2 mouse protocol extension to
 			probe for; one of (bare|imps|exps|lifebook|any).
 	psmouse.rate=	[HW,MOUSE] Set desired mouse report rate, in reports

include/linux/psi.h

@@ -14,6 +14,8 @@ struct css_set;
 extern struct static_key_false psi_disabled;
 extern struct psi_group psi_system;
 
+extern struct static_key_false psi_v1_disabled;
+
 void psi_init(void);
 
 void psi_task_change(struct task_struct *task, int clear, int set);

init/Kconfig

@@ -532,16 +532,6 @@ config PSI_DEFAULT_DISABLED
 
 	  Say N if unsure.
 
-config PSI_CGROUP_V1
-	bool "Support PSI under cgroup v1"
-	default Y
-	depends on PSI
-	help
-	  If set, pressure stall information tracking will be used
-	  for cgroup v1 other than v2.
-
-	  Say N if unsure.
-
 endmenu # "CPU/Task time and stats accounting"
 
 config CPU_ISOLATION

kernel/sched/cpuacct.c

@@ -375,8 +375,21 @@ struct cgroup_subsys cpuacct_cgrp_subsys = {
 };
 
 #ifdef CONFIG_PSI
+
+static bool psi_v1_enable;
+static int __init setup_psi_v1(char *str)
+{
+	return kstrtobool(str, &psi_v1_enable) == 0;
+}
+__setup("psi_v1=", setup_psi_v1);
+
 static int __init cgroup_v1_psi_init(void)
 {
+	if (!psi_v1_enable) {
+		static_branch_enable(&psi_v1_disabled);
+		return 0;
+	}
+
 	cgroup_add_legacy_cftypes(&cpuacct_cgrp_subsys, cgroup_v1_psi_files);
 	return 0;
 }

kernel/sched/psi.c

@@ -145,6 +145,7 @@
 static int psi_bug __read_mostly;
 
 DEFINE_STATIC_KEY_FALSE(psi_disabled);
+DEFINE_STATIC_KEY_FALSE(psi_v1_disabled);
 
 #ifdef CONFIG_PSI_DEFAULT_DISABLED
 static bool psi_enable;
@@ -724,13 +725,12 @@ static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
 #ifdef CONFIG_CGROUPS
 	struct cgroup *cgroup = NULL;
 
-	if (!*iter)
-#ifdef CONFIG_PSI_CGROUP_V1
-		cgroup = task_cgroup(task, cpuacct_cgrp_id);
-#else
-		cgroup = task->cgroups->dfl_cgrp;
-#endif
-	else if (*iter == &psi_system)
+	if (!*iter) {
+		if (static_branch_likely(&psi_v1_disabled))
+			cgroup = task->cgroups->dfl_cgrp;
+		else
+			cgroup = task_cgroup(task, cpuacct_cgrp_id);
+	} else if (*iter == &psi_system)
 		return NULL;
 	else
 		cgroup = cgroup_parent(*iter);