diff mbox series

[v5,11/18] timer: Split out "get next timer interrupt" functionality

Message ID 20230301141744.16063-12-anna-maria@linutronix.de
State New
Headers
Series timer: Move from a push remote at enqueue to a pull at expiry model |

Commit Message

Anna-Maria Behnsen March 1, 2023, 2:17 p.m. UTC 
  The functionallity for getting the next timer interrupt in
get_next_timer_interrupt() is splitted into a separate function
fetch_next_timer_interrupt() to be usable by other callsides.

This is preparatory work for the conversion of the NOHZ timer
placement to a pull at expiry time model. No functional change.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
---
v5: Update commit message
---
 kernel/time/timer.c | 91 +++++++++++++++++++++++++--------------------
 1 file changed, 50 insertions(+), 41 deletions(-)

Comments

Frederic Weisbecker March 9, 2023, 4:30 p.m. UTC | #1 
Le Wed, Mar 01, 2023 at 03:17:37PM +0100, Anna-Maria Behnsen a écrit :
> The functionallity for getting the next timer interrupt in
> get_next_timer_interrupt() is splitted into a separate function
> fetch_next_timer_interrupt() to be usable by other callsides.
> 
> This is preparatory work for the conversion of the NOHZ timer
> placement to a pull at expiry time model. No functional change.
> 
> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
[...]
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index ff41d978cb22..dfc744545159 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -2040,31 +2071,9 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
>  		if (time_before(nextevt, basej))
>  			nextevt = basej;
>  		tevt.local = basem + (u64)(nextevt - basej) * TICK_NSEC;
> -		goto unlock;
> +		tevt.global = KTIME_MAX;
>  	}
>  
> -	/*
> -	 * If the bases are marked idle, i.e. the next event on both the
> -	 * local and the global queue are farther away than a tick,
> -	 * evaluate both bases. No need to check whether one of the bases
> -	 * has an already expired timer as this is caught by the !is_idle
> -	 * condition above.
> -	 */
> -	if (base_local->timers_pending)
> -		tevt.local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
> -
> -	/*
> -	 * If the local queue expires first, then the global event can be
> -	 * ignored. The CPU wakes up before that. If the global queue is
> -	 * empty, nothing to do either.
> -	 */
> -	if (!local_first && base_global->timers_pending)
> -		tevt.global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
> -
> -unlock:
> -	raw_spin_unlock(&base_global->lock);
> -	raw_spin_unlock(&base_local->lock);
> -
>  	tevt.local = min_t(u64, tevt.local, tevt.global);

So if you leave that last line, it means that the CPU will eventually
and unconditionally wake up for the next global timer if it's before the
next local timer. Am I understanding this right and, if so, is that intended?

Thanks.
Frederic Weisbecker March 9, 2023, 5:45 p.m. UTC | #2 
On Thu, Mar 09, 2023 at 05:30:12PM +0100, Frederic Weisbecker wrote:
> Le Wed, Mar 01, 2023 at 03:17:37PM +0100, Anna-Maria Behnsen a écrit :
> > The functionallity for getting the next timer interrupt in
> > get_next_timer_interrupt() is splitted into a separate function
> > fetch_next_timer_interrupt() to be usable by other callsides.
> > 
> > This is preparatory work for the conversion of the NOHZ timer
> > placement to a pull at expiry time model. No functional change.
> > 
> > Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
> [...]
> > diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> > index ff41d978cb22..dfc744545159 100644
> > --- a/kernel/time/timer.c
> > +++ b/kernel/time/timer.c
> > @@ -2040,31 +2071,9 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
> >  		if (time_before(nextevt, basej))
> >  			nextevt = basej;
> >  		tevt.local = basem + (u64)(nextevt - basej) * TICK_NSEC;
> > -		goto unlock;
> > +		tevt.global = KTIME_MAX;
> >  	}
> >  
> > -	/*
> > -	 * If the bases are marked idle, i.e. the next event on both the
> > -	 * local and the global queue are farther away than a tick,
> > -	 * evaluate both bases. No need to check whether one of the bases
> > -	 * has an already expired timer as this is caught by the !is_idle
> > -	 * condition above.
> > -	 */
> > -	if (base_local->timers_pending)
> > -		tevt.local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
> > -
> > -	/*
> > -	 * If the local queue expires first, then the global event can be
> > -	 * ignored. The CPU wakes up before that. If the global queue is
> > -	 * empty, nothing to do either.
> > -	 */
> > -	if (!local_first && base_global->timers_pending)
> > -		tevt.global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
> > -
> > -unlock:
> > -	raw_spin_unlock(&base_global->lock);
> > -	raw_spin_unlock(&base_local->lock);
> > -
> >  	tevt.local = min_t(u64, tevt.local, tevt.global);
> 
> So if you leave that last line, it means that the CPU will eventually
> and unconditionally wake up for the next global timer if it's before the
> next local timer. Am I understanding this right and, if so, is that intended?

Nevermind, that's removed on the main patch.

Sorry for the noise.
Peter Zijlstra March 21, 2023, 2:30 p.m. UTC | #3 
On Wed, Mar 01, 2023 at 03:17:37PM +0100, Anna-Maria Behnsen wrote:
> The functionallity for getting the next timer interrupt in
> get_next_timer_interrupt() is splitted into a separate function

s/splitted/split/ -- also in other patches (8 iirc). Split is an
irregular verb and the past tense is the same as the present tense.
Frederic Weisbecker April 12, 2023, 8:34 p.m. UTC | #4 
Le Wed, Mar 01, 2023 at 03:17:37PM +0100, Anna-Maria Behnsen a écrit :
> The functionallity for getting the next timer interrupt in
> get_next_timer_interrupt() is splitted into a separate function
> fetch_next_timer_interrupt() to be usable by other callsides.
> 
> This is preparatory work for the conversion of the NOHZ timer
> placement to a pull at expiry time model. No functional change.
> 
> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
diff mbox series

Patch

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ff41d978cb22..dfc744545159 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1944,6 +1944,46 @@  static unsigned long next_timer_interrupt(struct timer_base *base)
 	return base->next_expiry;
 }
 
+static unsigned long fetch_next_timer_interrupt(struct timer_base *base_local,
+						struct timer_base *base_global,
+						unsigned long basej, u64 basem,
+						struct timer_events *tevt)
+{
+	unsigned long nextevt_local, nextevt_global;
+	bool local_first;
+
+	nextevt_local = next_timer_interrupt(base_local);
+	nextevt_global = next_timer_interrupt(base_global);
+
+	/*
+	 * Check whether the local event is expiring before or at the same
+	 * time as the global event.
+	 *
+	 * Note, that nextevt_global and nextevt_local might be based on
+	 * different base->clk values. So it's not guaranteed that
+	 * comparing with empty bases results in a correct local_first.
+	 */
+	if (base_local->timers_pending && base_global->timers_pending)
+		local_first = time_before_eq(nextevt_local, nextevt_global);
+	else
+		local_first = base_local->timers_pending;
+
+	/*
+	 * Update tevt->* values:
+	 *
+	 * If the local queue expires first, then the global event can
+	 * be ignored. If the global queue is empty, nothing to do
+	 * either.
+	 */
+	if (!local_first && base_global->timers_pending)
+		tevt->global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
+
+	if (base_local->timers_pending)
+		tevt->local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
+
+	return local_first ? nextevt_local : nextevt_global;
+}
+
 /*
  * Forward base clock is done only when @basej is past base->clk, otherwise
  * base-clk might be rewind.
@@ -1976,7 +2016,7 @@  u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 	struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
 	unsigned long nextevt, nextevt_local, nextevt_global;
 	struct timer_base *base_local, *base_global;
-	bool local_first, is_idle;
+	bool is_idle;
 
 	/*
 	 * Pretend that there is no timer pending if the cpu is offline.
@@ -1991,8 +2031,11 @@  u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 	raw_spin_lock(&base_local->lock);
 	raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
 
-	nextevt_local = next_timer_interrupt(base_local);
-	nextevt_global = next_timer_interrupt(base_global);
+	nextevt = fetch_next_timer_interrupt(base_local, base_global,
+					     basej, basem, &tevt);
+
+	nextevt_local = base_local->next_expiry;
+	nextevt_global = base_global->next_expiry;
 
 	/*
 	 * We have a fresh next event. Check whether we can forward the
@@ -2001,21 +2044,6 @@  u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 	forward_base_clk(base_local, nextevt_local, basej);
 	forward_base_clk(base_global, nextevt_global, basej);
 
-	/*
-	 * Check whether the local event is expiring before or at the same
-	 * time as the global event.
-	 *
-	 * Note, that nextevt_global and nextevt_local might be based on
-	 * different base->clk values. So it's not guaranteed that
-	 * comparing with empty bases results in a correct local_first.
-	 */
-	if (base_local->timers_pending && base_global->timers_pending)
-		local_first = time_before_eq(nextevt_local, nextevt_global);
-	else
-		local_first = base_local->timers_pending;
-
-	nextevt = local_first ? nextevt_local : nextevt_global;
-
 	/*
 	 * Bases are idle if the next event is more than a tick away. Also
 	 * the tick is stopped so any added timer must forward the base clk
@@ -2028,6 +2056,9 @@  u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 	/* We need to mark both bases in sync */
 	base_local->is_idle = base_global->is_idle = is_idle;
 
+	raw_spin_unlock(&base_global->lock);
+	raw_spin_unlock(&base_local->lock);
+
 	/*
 	 * If the bases are not marked idle, i.e one of the events is at
 	 * max. one tick away, then the CPU can't go into a NOHZ idle
@@ -2040,31 +2071,9 @@  u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 		if (time_before(nextevt, basej))
 			nextevt = basej;
 		tevt.local = basem + (u64)(nextevt - basej) * TICK_NSEC;
-		goto unlock;
+		tevt.global = KTIME_MAX;
 	}
 
-	/*
-	 * If the bases are marked idle, i.e. the next event on both the
-	 * local and the global queue are farther away than a tick,
-	 * evaluate both bases. No need to check whether one of the bases
-	 * has an already expired timer as this is caught by the !is_idle
-	 * condition above.
-	 */
-	if (base_local->timers_pending)
-		tevt.local = basem + (u64)(nextevt_local - basej) * TICK_NSEC;
-
-	/*
-	 * If the local queue expires first, then the global event can be
-	 * ignored. The CPU wakes up before that. If the global queue is
-	 * empty, nothing to do either.
-	 */
-	if (!local_first && base_global->timers_pending)
-		tevt.global = basem + (u64)(nextevt_global - basej) * TICK_NSEC;
-
-unlock:
-	raw_spin_unlock(&base_global->lock);
-	raw_spin_unlock(&base_local->lock);
-
 	tevt.local = min_t(u64, tevt.local, tevt.global);
 
 	return cmp_next_hrtimer_event(basem, tevt.local);