1 files changed, 40 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 9b302e35579..9e01b7100ef 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -491,6 +491,7 @@ struct rq {
 	struct mm_struct *prev_mm;
 
 	u64 clock;
+	u64 clock_task;
 
 	atomic_t nr_iowait;
 
@@ -641,10 +642,19 @@ static inline struct task_group *task_group(struct task_struct *p)
 
 #endif /* CONFIG_CGROUP_SCHED */
 
+static u64 irq_time_cpu(int cpu);
+
 inline void update_rq_clock(struct rq *rq)
 {
-	if (!rq->skip_clock_update)
-		rq->clock = sched_clock_cpu(cpu_of(rq));
+	if (!rq->skip_clock_update) {
+		int cpu = cpu_of(rq);
+		u64 irq_time;
+
+		rq->clock = sched_clock_cpu(cpu);
+		irq_time = irq_time_cpu(cpu);
+		if (rq->clock - irq_time > rq->clock_task)
+			rq->clock_task = rq->clock - irq_time;
+	}
 }
 
 /*
@@ -1910,6 +1920,18 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 
+/*
+ * There are no locks covering percpu hardirq/softirq time.
+ * They are only modified in account_system_vtime, on corresponding CPU
+ * with interrupts disabled. So, writes are safe.
+ * They are read and saved off onto struct rq in update_rq_clock().
+ * This may result in other CPU reading this CPU's irq time and can
+ * race with irq/account_system_vtime on this CPU. We would either get old
+ * or new value (or semi updated value on 32 bit) with a side effect of
+ * accounting a slice of irq time to wrong task when irq is in progress
+ * while we read rq->clock. That is a worthy compromise in place of having
+ * locks on each irq in account_system_time.
+ */
 static DEFINE_PER_CPU(u64, cpu_hardirq_time);
 static DEFINE_PER_CPU(u64, cpu_softirq_time);
 
@@ -1926,6 +1948,14 @@ void disable_sched_clock_irqtime(void)
 	sched_clock_irqtime = 0;
 }
 
+static u64 irq_time_cpu(int cpu)
+{
+	if (!sched_clock_irqtime)
+		return 0;
+
+	return per_cpu(cpu_softirq_time, cpu) + per_cpu(cpu_hardirq_time, cpu);
+}
+
 void account_system_vtime(struct task_struct *curr)
 {
 	unsigned long flags;
@@ -1955,6 +1985,13 @@ void account_system_vtime(struct task_struct *curr)
 	local_irq_restore(flags);
 }
 
+#else
+
+static u64 irq_time_cpu(int cpu)
+{
+	return 0;
+}
+
 #endif
 
 #include "sched_idletask.c"
@@ -3322,7 +3359,7 @@ static u64 do_task_delta_exec(struct task_struct *p, struct rq *rq)
 
 	if (task_current(rq, p)) {
 		update_rq_clock(rq);
-		ns = rq->clock - p->se.exec_start;
+		ns = rq->clock_task - p->se.exec_start;
 		if ((s64)ns < 0)
 			ns = 0;
 	}