[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20200701011030.14324-8-frederic@kernel.org>
Date: Wed, 1 Jul 2020 03:10:27 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Frederic Weisbecker <frederic@...nel.org>,
Anna-Maria Gleixner <anna-maria@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>
Subject: [RFC PATCH 07/10] timer: Expand clk forward logic beyond nohz
As for next_expiry, we want to expand base->clk catch up logic beyond
nohz in order to avoid triggering useless softirqs.
If we want to fire softirqs only to expire pending timers, periodic
base->clk increments must be skippable for random amounts of time.
Therefore we must prepare to catch-up with missing updates whenever we
need an up-to-date base clock.
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc: Juri Lelli <juri.lelli@...hat.com>
---
kernel/time/timer.c | 26 ++++----------------------
1 file changed, 4 insertions(+), 22 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 4612d26fd09a..6c021be0e76f 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -877,19 +877,12 @@ get_target_base(struct timer_base *base, unsigned tflags)
static inline void forward_timer_base(struct timer_base *base)
{
-#ifdef CONFIG_NO_HZ_COMMON
unsigned long jnow;
- /*
- * We only forward the base when we are idle or have just come out of
- * idle (must_forward_clk logic), and have a delta between base clock
- * and jiffies. In the common case, run_timers will take care of it.
- */
- if (likely(!base->must_forward_clk))
+ if (!base->must_forward_clk)
return;
jnow = READ_ONCE(jiffies);
- base->must_forward_clk = base->is_idle;
if ((long)(jnow - base->clk) < 2)
return;
@@ -904,7 +897,6 @@ static inline void forward_timer_base(struct timer_base *base)
return;
base->clk = base->next_expiry;
}
-#endif
}
@@ -1658,10 +1650,8 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
* logic is only maintained for the BASE_STD base, deferrable
* timers may still see large granularity skew (by design).
*/
- if ((expires - basem) > TICK_NSEC) {
- base->must_forward_clk = true;
+ if ((expires - basem) > TICK_NSEC)
base->is_idle = true;
- }
}
raw_spin_unlock(&base->lock);
@@ -1760,16 +1750,7 @@ static inline void __run_timers(struct timer_base *base)
/*
* 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. Idle tracking / clock forwarding
- * logic is only used with BASE_STD timers.
- *
- * The must_forward_clk flag is cleared unconditionally also for
- * the deferrable base. The deferrable base is not affected by idle
- * tracking and never forwarded, so clearing the flag is a NOOP.
- *
- * The fact that the deferrable base is never forwarded can cause
- * large variations in granularity for deferrable timers, but they
- * can be deferred for long periods due to idle anyway.
+ * not try to forward the base.
*/
base->must_forward_clk = false;
@@ -1782,6 +1763,7 @@ 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);
}
--
2.26.2
Powered by blists - more mailing lists