[PATCH v2 5/5] sched, timer: Use the atomic task_cputime in thread_group_cputimer

[Jason Low]

Recent optimizations were made to thread_group_cputimer to improve its
scalability by keeping track of cputime stats without a lock. However,
the values were open coded to the structure, causing them to be at
a different abstraction level from the regular task_cputime structure.
Furthermore, any subsequent similar optimizations would not be able to
share the new code, since they are specific to thread_group_cputimer.
 
This patch adds the new task_cputime_atomic data structure (introduced in
the previous patch in the series) to thread_group_cputimer for keeping
track of the cputime atomically, which also helps generalize the code.

Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Jason Low <jason.low2@xxxxxx>
---
 include/linux/init_task.h      |    6 ++----
 include/linux/sched.h          |    4 +---
 kernel/sched/stats.h           |    6 +++---
 kernel/time/posix-cpu-timers.c |   26 +++++++++++++-------------
 4 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 7b9d8b5..bb9b075 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -50,10 +50,8 @@ extern struct fs_struct init_fs;
 	.cpu_timers	= INIT_CPU_TIMERS(sig.cpu_timers),		\
 	.rlim		= INIT_RLIMITS,					\
 	.cputimer	= { 						\
-		.utime 		  = ATOMIC64_INIT(0),			\
-		.stime		  = ATOMIC64_INIT(0),			\
-		.sum_exec_runtime = ATOMIC64_INIT(0),			\
-		.running 	  = 0					\
+		.cputime_atomic	= INIT_CPUTIME_ATOMIC,			\
+		.running	= 0,					\
 	},								\
 	.cred_guard_mutex =						\
 		 __MUTEX_INITIALIZER(sig.cred_guard_mutex),		\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7092192..80ce921c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -618,9 +618,7 @@ struct task_cputime_atomic {
  * used for thread group CPU timer calculations.
  */
 struct thread_group_cputimer {
-	atomic64_t utime;
-	atomic64_t stime;
-	atomic64_t sum_exec_runtime;
+	struct task_cputime_atomic cputime_atomic;
 	int running;
 };
 
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index c6d1c7d..077ebbd 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -216,7 +216,7 @@ static inline void account_group_user_time(struct task_struct *tsk,
 	if (!cputimer_running(tsk))
 		return;
 
-	atomic64_add(cputime, &cputimer->utime);
+	atomic64_add(cputime, &cputimer->cputime_atomic.utime);
 }
 
 /**
@@ -237,7 +237,7 @@ static inline void account_group_system_time(struct task_struct *tsk,
 	if (!cputimer_running(tsk))
 		return;
 
-	atomic64_add(cputime, &cputimer->stime);
+	atomic64_add(cputime, &cputimer->cputime_atomic.stime);
 }
 
 /**
@@ -258,5 +258,5 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
 	if (!cputimer_running(tsk))
 		return;
 
-	atomic64_add(ns, &cputimer->sum_exec_runtime);
+	atomic64_add(ns, &cputimer->cputime_atomic.sum_exec_runtime);
 }
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index d857306..892e3da 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -211,20 +211,20 @@ retry:
 	}
 }
 
-static void update_gt_cputime(struct thread_group_cputimer *cputimer, struct task_cputime *sum)
+static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic, struct task_cputime *sum)
 {
-	__update_gt_cputime(&cputimer->utime, sum->utime);
-	__update_gt_cputime(&cputimer->stime, sum->stime);
-	__update_gt_cputime(&cputimer->sum_exec_runtime, sum->sum_exec_runtime);
+	__update_gt_cputime(&cputime_atomic->utime, sum->utime);
+	__update_gt_cputime(&cputime_atomic->stime, sum->stime);
+	__update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
 }
 
-/* Sample thread_group_cputimer values in "cputimer", store results in "times". */
-static inline void sample_group_cputimer(struct task_cputime *times,
-					  struct thread_group_cputimer *cputimer)
+/* Sample task_cputime_atomic values in "atomic_timers", store results in "times". */
+static inline void sample_cputime_atomic(struct task_cputime *times,
+					 struct task_cputime_atomic *atomic_times)
 {
-	times->utime = atomic64_read(&cputimer->utime);
-	times->stime = atomic64_read(&cputimer->stime);
-	times->sum_exec_runtime = atomic64_read(&cputimer->sum_exec_runtime);
+	times->utime = atomic64_read(&atomic_times->utime);
+	times->stime = atomic64_read(&atomic_times->stime);
+	times->sum_exec_runtime = atomic64_read(&atomic_times->sum_exec_runtime);
 }
 
 void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
@@ -240,7 +240,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
 		 * to synchronize the timer to the clock every time we start it.
 		 */
 		thread_group_cputime(tsk, &sum);
-		update_gt_cputime(cputimer, &sum);
+		update_gt_cputime(&cputimer->cputime_atomic, &sum);
 
 		/*
 		 * We're setting cputimer->running without a lock. Ensure
@@ -251,7 +251,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
 		 */
 		WRITE_ONCE(cputimer->running, 1);
 	}
-	sample_group_cputimer(times, cputimer);
+	sample_cputime_atomic(times, &cputimer->cputime_atomic);
 }
 
 /*
@@ -1137,7 +1137,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
 	if (READ_ONCE(sig->cputimer.running)) {
 		struct task_cputime group_sample;
 
-		sample_group_cputimer(&group_sample, &sig->cputimer);
+		sample_cputime_atomic(&group_sample, &sig->cputimer.cputime_atomic);
 
 		if (task_cputime_expired(&group_sample, &sig->cputime_expires))
 			return 1;
-- 
1.7.2.5

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