Re: [PATCH] Clean up of hrtimer code.

[Thomas Gleixner]

George,

On Wed, 2006-01-18 at 17:54 -0800, George Anzinger wrote:
> Description:
> 
> This patch cleans up the interface to hrtimers by changing the init code
> to pass the mode as well as the clock.  This allow the init code to
> select the correct base and eliminates extra timer re-init code in
> posix-timers.  We also simplify the restart interface by defining a
> restart union with an entry for nanosleep use.

Thanks. I revamped it against mainline and picked up most of your
changes with a couple of modifications.

Will show up later tonight in the hrtimer-git repository on kernel.org
when I finished testing.

	tglx

> +/**
> + * We want to use the "monotonic" base for everything except
> + * CLOCK_REALTIME* with the absolute flag set.  We need to
> + * account for the hole in the clocks caused by the CPU clocks
> + * (sigh).  We could use a case statement or, depend on REALTIME
> + * clocks being even and MONOTONIC being odd.  This even allow us
> + * to expand easily beyond 2 clocks.
> + *
> + */
> +#define _clock_to_base(clock) (clock <= CLOCK_MONOTONIC ? clock : clock - 2)
> +int clock_to_base_index(clock_t clock, enum hrtimer_mode mode)
> +{
> +	int baseindex = _clock_to_base(clock);
> +
> +	if (mode == HRTIMER_ABS)
> +		return baseindex;
> +	return baseindex | 1;
> +}

I skipped this, as I prefer that we add two unused entries into the base
array for following reasons:

If the code gets called with one of the skipped clock_ids, the magic
adjustment corrects them to a valid clock id and we certainly could get
some hard to track problems that way.

The assumption that the CLOCK_REALTIME/MONOTONIC relationship is valid
for all additional clocks is not correct.

>  /**
>   * hrtimer_init - initialize a timer to the given clock
>   *
>   * @timer:	the timer to be initialized
>   * @clock_id:	the clock to be used
> - */
> -void hrtimer_init(struct hrtimer *timer, const clockid_t clock_id)
> +  * mode:        HRTIMER_ABS if absolute mode
> +*/
> +void hrtimer_init(struct hrtimer *timer, const clockid_t clock_id,
> +		  enum hrtimer_mode mode)
>  {
> +	struct hrtimer_base *bases =
> +		per_cpu(hrtimer_bases, raw_smp_processor_id());
> +
>  	memset(timer, 0, sizeof(struct hrtimer));
> -	hrtimer_rebase(timer, clock_id);
> +	timer->base = &bases[clock_to_base_index(clock_id, mode)];
>  }

Changed that to the rules above.
 
 
> -	restart = &current_thread_info()->restart_block;
> -	restart->fn = (clockid == CLOCK_MONOTONIC) ?
> -		nanosleep_restart_mono : nanosleep_restart_real;
> -	restart->arg0 = timer.expires.tv64 & 0xFFFFFFFF;
> -	restart->arg1 = timer.expires.tv64 >> 32;
> -	restart->arg2 = (unsigned long) rmtp;
> +	restart = (union restart_union *)&current_thread_info()->restart_block;
> +	restart->ns.fn = nanosleep_restart;
> +	restart->ns.time = timer.expires;
> +	restart->ns.rmtp = rmtp;
> +	restart->ns.mode = (unsigned char)mode;
> +	restart->ns.clock = (unsigned char)clockid;

Adding 

	restart->arg3 = timer.base->index;

is just enough. No need for creating this union thingy. The mode
information is not necessary, as the timer is always restarted in
absolute mode with the existing expires value on the previous base.


>  	return -ERESTART_RESTARTBLOCK;
>  }
> Index: linux-2.6.16-rc/kernel/posix-timers.c
> ===================================================================
> --- linux-2.6.16-rc.orig/kernel/posix-timers.c
> +++ linux-2.6.16-rc/kernel/posix-timers.c
> @@ -194,9 +194,6 @@ static inline int common_clock_set(const
>  
>  static inline int common_timer_create(struct k_itimer *new_timer)
>  {
> -	hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock);

I kept that init as a dummy one. Thats simpler than adding all the 
if(!base) stuff into the hrtimer code. Not having those checks gives a
nice oops, when somebody tries to access a non initialized hrtimer !

George, thats the current revamped version against 2.6.16-rc1:

include/linux/hrtimer.h |    5 +---
 kernel/fork.c           |    2 -
 kernel/hrtimer.c        |   57 +++++++++++++++++++-----------------------------
 kernel/posix-timers.c   |   37 +++++++------------------------
 4 files changed, 35 insertions(+), 66 deletions(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index c657f3d..6361544 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -101,9 +101,8 @@ struct hrtimer_base {
 /* Exported timer functions: */
 
 /* Initialize timers: */
-extern void hrtimer_init(struct hrtimer *timer, const clockid_t which_clock);
-extern void hrtimer_rebase(struct hrtimer *timer, const clockid_t which_clock);
-
+extern void hrtimer_init(struct hrtimer *timer, clockid_t which_clock,
+			 enum hrtimer_mode mode);
 
 /* Basic timer operations: */
 extern int hrtimer_start(struct hrtimer *timer, ktime_t tim,
diff --git a/kernel/fork.c b/kernel/fork.c
index 4ae8cfc..7f0ab5e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -802,7 +802,7 @@ static inline int copy_signal(unsigned l
 	init_sigpending(&sig->shared_pending);
 	INIT_LIST_HEAD(&sig->posix_timers);
 
-	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC);
+	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_REL);
 	sig->it_real_incr.tv64 = 0;
 	sig->real_timer.function = it_real_fn;
 	sig->real_timer.data = tsk;
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index f580dd9..383ef7b 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -66,6 +66,12 @@ EXPORT_SYMBOL_GPL(ktime_get_real);
 
 /*
  * The timer bases:
+ *
+ * Note: If we want to add new timer bases, we have to skip the two
+ * clock ids captured by the cpu-timers. We do this by holding empty
+ * entries rather than doing math adjustment of the clock ids.
+ * This ensures that we capture erroneous accesses to these clock ids
+ * rather than moving them into the range of valid clock id's.
  */
 
 #define MAX_HRTIMER_BASES 2
@@ -483,29 +489,25 @@ ktime_t hrtimer_get_remaining(const stru
 }
 
 /**
- * hrtimer_rebase - rebase an initialized hrtimer to a different base
+ * hrtimer_init - initialize a timer to the given clock
  *
- * @timer:	the timer to be rebased
+ * @timer:	the timer to be initialized
  * @clock_id:	the clock to be used
+ * @mode:	timer mode abs/rel
  */
-void hrtimer_rebase(struct hrtimer *timer, const clockid_t clock_id)
+void hrtimer_init(struct hrtimer *timer, clockid_t clock_id, 
+		  enum hrtimer_mode mode)
 {
 	struct hrtimer_base *bases;
 
+	memset(timer, 0, sizeof(struct hrtimer));
+
 	bases = per_cpu(hrtimer_bases, raw_smp_processor_id());
-	timer->base = &bases[clock_id];
-}
 
-/**
- * hrtimer_init - initialize a timer to the given clock
- *
- * @timer:	the timer to be initialized
- * @clock_id:	the clock to be used
- */
-void hrtimer_init(struct hrtimer *timer, const clockid_t clock_id)
-{
-	memset(timer, 0, sizeof(struct hrtimer));
-	hrtimer_rebase(timer, clock_id);
+	if (clock_id == CLOCK_REALTIME && mode != HRTIMER_ABS)
+		clock_id = CLOCK_MONOTONIC;
+
+	timer->base = &bases[clock_id];
 }
 
 /**
@@ -643,8 +645,7 @@ schedule_hrtimer_interruptible(struct hr
 	return schedule_hrtimer(timer, mode);
 }
 
-static long __sched
-nanosleep_restart(struct restart_block *restart, clockid_t clockid)
+static long __sched nanosleep_restart(struct restart_block *restart)
 {
 	struct timespec __user *rmtp;
 	struct timespec tu;
@@ -654,7 +655,7 @@ nanosleep_restart(struct restart_block *
 
 	restart->fn = do_no_restart_syscall;
 
-	hrtimer_init(&timer, clockid);
+	hrtimer_init(&timer, (clockid_t) restart->arg3, HRTIMER_ABS);
 
 	timer.expires.tv64 = ((u64)restart->arg1 << 32) | (u64) restart->arg0;
 
@@ -674,16 +675,6 @@ nanosleep_restart(struct restart_block *
 	return -ERESTART_RESTARTBLOCK;
 }
 
-static long __sched nanosleep_restart_mono(struct restart_block *restart)
-{
-	return nanosleep_restart(restart, CLOCK_MONOTONIC);
-}
-
-static long __sched nanosleep_restart_real(struct restart_block *restart)
-{
-	return nanosleep_restart(restart, CLOCK_REALTIME);
-}
-
 long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
 		       const enum hrtimer_mode mode, const clockid_t clockid)
 {
@@ -692,7 +683,7 @@ long hrtimer_nanosleep(struct timespec *
 	struct timespec tu;
 	ktime_t rem;
 
-	hrtimer_init(&timer, clockid);
+	hrtimer_init(&timer, clockid, mode);
 
 	timer.expires = timespec_to_ktime(*rqtp);
 
@@ -710,11 +701,11 @@ long hrtimer_nanosleep(struct timespec *
 		return -EFAULT;
 
 	restart = &current_thread_info()->restart_block;
-	restart->fn = (clockid == CLOCK_MONOTONIC) ?
-		nanosleep_restart_mono : nanosleep_restart_real;
+	restart->fn = nanosleep_restart;
 	restart->arg0 = timer.expires.tv64 & 0xFFFFFFFF;
 	restart->arg1 = timer.expires.tv64 >> 32;
 	restart->arg2 = (unsigned long) rmtp;
+	restart->arg3 = (unsigned long) timer.base->index;
 
 	return -ERESTART_RESTARTBLOCK;
 }
@@ -741,10 +732,8 @@ static void __devinit init_hrtimers_cpu(
 	struct hrtimer_base *base = per_cpu(hrtimer_bases, cpu);
 	int i;
 
-	for (i = 0; i < MAX_HRTIMER_BASES; i++) {
+	for (i = 0; i < MAX_HRTIMER_BASES; i++, base++)
 		spin_lock_init(&base->lock);
-		base++;
-	}
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 3b606d3..54f0866 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -194,9 +194,7 @@ static inline int common_clock_set(const
 
 static int common_timer_create(struct k_itimer *new_timer)
 {
-	hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock);
-	new_timer->it.real.timer.data = new_timer;
-	new_timer->it.real.timer.function = posix_timer_fn;
+	hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0);
 	return 0;
 }
 
@@ -693,6 +691,7 @@ common_timer_set(struct k_itimer *timr, 
 		 struct itimerspec *new_setting, struct itimerspec *old_setting)
 {
 	struct hrtimer *timer = &timr->it.real.timer;
+	enum hrtimer_mode mode;
 
 	if (old_setting)
 		common_timer_get(timr, old_setting);
@@ -714,14 +713,10 @@ common_timer_set(struct k_itimer *timr, 
 	if (!new_setting->it_value.tv_sec && !new_setting->it_value.tv_nsec)
 		return 0;
 
-	/* Posix madness. Only absolute CLOCK_REALTIME timers
-	 * are affected by clock sets. So we must reiniatilize
-	 * the timer.
-	 */
-	if (timr->it_clock == CLOCK_REALTIME && (flags & TIMER_ABSTIME))
-		hrtimer_rebase(timer, CLOCK_REALTIME);
-	else
-		hrtimer_rebase(timer, CLOCK_MONOTONIC);
+	mode = flags & TIMER_ABSTIME ? HRTIMER_ABS : HRTIMER_REL;
+	hrtimer_init(&timr->it.real.timer, timr->it_clock, mode);
+	timr->it.real.timer.data = timr;
+	timr->it.real.timer.function = posix_timer_fn;
 
 	timer->expires = timespec_to_ktime(new_setting->it_value);
 
@@ -732,8 +727,7 @@ common_timer_set(struct k_itimer *timr, 
 	if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE))
 		return 0;
 
-	hrtimer_start(timer, timer->expires, (flags & TIMER_ABSTIME) ?
-		      HRTIMER_ABS : HRTIMER_REL);
+	hrtimer_start(timer, timer->expires, mode);
 	return 0;
 }
 
@@ -948,21 +942,8 @@ sys_clock_getres(const clockid_t which_c
 static int common_nsleep(const clockid_t which_clock, int flags,
 			 struct timespec *tsave, struct timespec __user *rmtp)
 {
-	int mode = flags & TIMER_ABSTIME ? HRTIMER_ABS : HRTIMER_REL;
-	int clockid = which_clock;
-
-	switch (which_clock) {
-	case CLOCK_REALTIME:
-		/* Posix madness. Only absolute timers on clock realtime
-		   are affected by clock set. */
-		if (mode != HRTIMER_ABS)
-			clockid = CLOCK_MONOTONIC;
-	case CLOCK_MONOTONIC:
-		break;
-	default:
-		return -EINVAL;
-	}
-	return hrtimer_nanosleep(tsave, rmtp, mode, clockid);
+	return hrtimer_nanosleep(tsave, rmtp, flags & TIMER_ABSTIME ?
+				 HRTIMER_ABS : HRTIMER_REL, which_clock);
 }
 
 asmlinkage long
 



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