[RFC PATCH 09/10] timer: Remove must_forward_clk

Frederic Weisbecker
2020-07-01T01:10:55Z

There is no reason to keep this guard around. The code makes sure that
base->clk remains sane and won't be forwarded beyond jiffies nor set
backward.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
---
kernel/time/timer.c | 22 ++++++----------------
1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 95f51b646447..439fee098e76 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -204,7 +204,6 @@ struct timer_base {
unsigned long next_expiry;
unsigned int cpu;
bool is_idle;
- bool must_forward_clk;
DECLARE_BITMAP(pending_map, WHEEL_SIZE);
struct hlist_head vectors[WHEEL_SIZE];
} ____cacheline_aligned;
@@ -877,12 +876,13 @@ get_target_base(struct timer_base *base, unsigned tflags)

static inline void forward_timer_base(struct timer_base *base)
{
- unsigned long jnow;
+ unsigned long jnow = READ_ONCE(jiffies);

- if (!base->must_forward_clk)
- return;
-
- jnow = READ_ONCE(jiffies);
+ /*
+ * No need to forward if we are close enough below jiffies.
+ * Also while executing timers, base->clk is 1 offset ahead
+ * of jiffies to avoid endless requeuing to current jffies.
+ */
if ((long)(jnow - base->clk) < 2)
return;

@@ -1713,16 +1713,8 @@ static inline void __run_timers(struct timer_base *base)
timer_base_lock_expiry(base);
raw_spin_lock_irq(&base->lock);

- /*
- * timer_base::must_forward_clk must be cleared before running
- * timers so that any timer functions that call mod_timer() will
- * not try to forward the base.
- */
- base->must_forward_clk = false;
-
while (time_after_eq(jiffies, base->clk) &&
time_after_eq(jiffies, base->next_expiry)) {
-
levels = collect_expired_timers(base, heads);
base->clk++;
base->next_expiry = __next_timer_interrupt(base);
@@ -1730,7 +1722,6 @@ static inline void __run_timers(struct timer_base *base)
while (levels--)
expire_timers(base, heads + levels);
}
- base->must_forward_clk = true;
raw_spin_unlock_irq(&base->lock);
timer_base_unlock_expiry(base);
}
@@ -1926,7 +1917,6 @@ int timers_prepare_cpu(unsigned int cpu)
base->clk = jiffies;
base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
base->is_idle = false;
- base->must_forward_clk = true;
}
return 0;
}
--
2.26.2