[PATCH 12/13] hrtimer: optimize hrtimer_get_remaining

[PATCH 12/13] hrtimer: optimize hrtimer_get_remaining

[Roman Zippel]

hrtimer_get_remaining doesn't need to lock the hrtimer_base to read the
time. Also use hrtimer_get_remaining at two other places.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>

 kernel/hrtimer.c |   18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

Index: linux-2.6-git/kernel/hrtimer.c
===================================================================
--- linux-2.6-git.orig/kernel/hrtimer.c	2006-02-13 01:39:19.000000000 +0100
+++ linux-2.6-git/kernel/hrtimer.c	2006-02-13 01:41:59.000000000 +0100
@@ -482,15 +482,7 @@ int hrtimer_cancel(struct hrtimer *timer
  */
 ktime_t hrtimer_get_remaining(const struct hrtimer *timer)
 {
-	struct hrtimer_base *base;
-	unsigned long flags;
-	ktime_t rem;
-
-	base = lock_hrtimer_base(timer, &flags);
-	rem = ktime_sub(timer->expires, timer->base->get_time());
-	unlock_hrtimer_base(timer, &flags);
-
-	return rem;
+	return ktime_sub(timer->expires, timer->base->get_time());
 }
 
 /**
@@ -639,7 +631,6 @@ static long __sched nanosleep_restart(st
 	struct sleep_hrtimer t;
 	struct timespec __user *rmtp;
 	struct timespec tu;
-	ktime_t time;
 
 	restart->fn = do_no_restart_syscall;
 
@@ -650,8 +641,7 @@ static long __sched nanosleep_restart(st
 
 	rmtp = (struct timespec __user *) restart->arg2;
 	if (rmtp) {
-		time = ktime_sub(t.timer.expires, t.timer.base->get_time());
-		tu = ktime_to_timespec(time);
+		tu = ktime_to_timespec(hrtimer_get_remaining(&t.timer));
 		if (copy_to_user(rmtp, &tu, sizeof(tu)))
 			return -EFAULT;
 	}
@@ -668,7 +658,6 @@ long hrtimer_nanosleep(struct timespec *
 	struct restart_block *restart;
 	struct sleep_hrtimer t;
 	struct timespec tu;
-	ktime_t rem;
 
 	hrtimer_init(&t.timer, clockid, mode);
 	t.timer.expires = timespec_to_ktime(*rqtp);
@@ -680,8 +669,7 @@ long hrtimer_nanosleep(struct timespec *
 		return -ERESTARTNOHAND;
 
 	if (rmtp) {
-		rem = ktime_sub(t.timer.expires, t.timer.base->get_time());
-		tu = ktime_to_timespec(rem);
+		tu = ktime_to_timespec(hrtimer_get_remaining(&t.timer));
 		if (copy_to_user(rmtp, &tu, sizeof(tu)))
 			return -EFAULT;
 	}

Re: [PATCH 12/13] hrtimer: optimize hrtimer_get_remaining

[Ingo Molnar]

* Roman Zippel <zippel@linux-m68k.org> wrote:

> hrtimer_get_remaining doesn't need to lock the hrtimer_base to read 
> the time. Also use hrtimer_get_remaining at two other places.

nack - it's not only about ->get_time() atomicity:

> -	base = lock_hrtimer_base(timer, &flags);
> -	rem = ktime_sub(timer->expires, timer->base->get_time());
> -	unlock_hrtimer_base(timer, &flags);

timer->expires is a 64-bit value, which might be read nonatomically on 
32-bit platforms. Wherever it's safe, we already open-code this 
ktime_sub() - if you find more places then please do it that way.

definitely not something for v2.6.16.

	Ingo