[PATCH, v10 1/3] hrtimer: introduce effective timer slack

@@ -69,7 +69,6 @@ static long __estimate_accuracy(struct timespec *tv)
 
 long select_estimate_accuracy(struct timespec *tv)
 {
-	unsigned long ret;
 	struct timespec now;
 
 	/*

@@ -81,10 +80,8 @@ long select_estimate_accuracy(struct timespec *tv)
 
 	ktime_get_ts(&now);
 	now = timespec_sub(*tv, now);
-	ret = __estimate_accuracy(&now);
-	if (ret < current->timer_slack_ns)
-		return current->timer_slack_ns;
-	return ret;
+	return min_t(long, __estimate_accuracy(&now),
+			task_get_effective_timer_slack(current));
 }
 
 

@@ -2719,6 +2719,12 @@ static inline unsigned long rlimit_max(unsigned int limit)
 	return task_rlimit_max(current, limit);
 }
 
+static inline unsigned long task_get_effective_timer_slack(
+		struct task_struct *tsk)
+{
+	return tsk->timer_slack_ns;
+}
+
 #endif /* __KERNEL__ */
 
 #endif

@@ -1180,6 +1180,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
 #endif
 
+	/*
+	 * Save current task's (not effective) timer slack value as default
+	 * timer slack value for new task.
+	 */
 	p->default_timer_slack_ns = current->timer_slack_ns;
 
 	task_io_accounting_init(&p->ioac);

@@ -1875,7 +1875,7 @@ static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
 				      HRTIMER_MODE_ABS);
 		hrtimer_init_sleeper(to, current);
 		hrtimer_set_expires_range_ns(&to->timer, *abs_time,
-					     current->timer_slack_ns);
+				     task_get_effective_timer_slack(current));
 	}
 
 retry:

@@ -2269,7 +2269,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 				      HRTIMER_MODE_ABS);
 		hrtimer_init_sleeper(to, current);
 		hrtimer_set_expires_range_ns(&to->timer, *abs_time,
-					     current->timer_slack_ns);
+				     task_get_effective_timer_slack(current));
 	}
 
 	/*

@@ -1562,7 +1562,7 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
 	int ret = 0;
 	unsigned long slack;
 
-	slack = current->timer_slack_ns;
+	slack = task_get_effective_timer_slack(current);
 	if (rt_task(current))
 		slack = 0;