[RFC PATCH 1/7] cgroup: add cgroup_account_system_time()

[Shakeel Butt <shakeel.butt@linux.dev>]

Add a helper that charges some kernel CPU time to a cgroup's cpu.stat.
The next patch uses it for the time a kernel thread spends working for
another cgroup.

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 include/linux/cgroup.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 2afb4cb2bb4f..7b19ded2578d 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -868,6 +868,17 @@ void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec);
 void __cgroup_account_cputime_field(struct cgroup *cgrp,
 				    enum cpu_usage_stat index, u64 delta_exec);
 
+/* Charge @delta_exec of kernel CPU time to @cgrp. */
+static inline void cgroup_account_system_time(struct cgroup *cgrp,
+					      u64 delta_exec)
+{
+	if (cgroup_parent(cgrp)) {
+		__cgroup_account_cputime(cgrp, delta_exec);
+		__cgroup_account_cputime_field(cgrp, CPUTIME_SYSTEM,
+					       delta_exec);
+	}
+}
+
 static inline void cgroup_account_cputime(struct task_struct *task,
 					  u64 delta_exec)
 {
@@ -900,6 +911,8 @@ static inline void cgroup_account_cputime(struct task_struct *task,
 static inline void cgroup_account_cputime_field(struct task_struct *task,
 						enum cpu_usage_stat index,
 						u64 delta_exec) {}
+static inline void cgroup_account_system_time(struct cgroup *cgrp,
+					      u64 delta_exec) {}
 
 #endif	/* CONFIG_CGROUPS */
 
-- 
2.53.0-Meta