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Message-ID: <170862192461.398.10613375933312669358.tip-bot2@tip-bot2>
Date: Thu, 22 Feb 2024 17:12:04 -0000
From: "tip-bot2 for Anna-Maria Behnsen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Richard Cochran (linutronix GmbH)" <richardcochran@...il.com>,
"Anna-Maria Behnsen" <anna-maria@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>,
Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timers: Always queue timers on the local CPU
The following commit has been merged into the timers/core branch of tip:
Commit-ID: b2cf7507e18649a30512515ec0ca89f26b2c2d0f
Gitweb: https://git.kernel.org/tip/b2cf7507e18649a30512515ec0ca89f26b2c2d0f
Author: Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate: Wed, 21 Feb 2024 10:05:48 +01:00
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 22 Feb 2024 17:52:32 +01:00
timers: Always queue timers on the local CPU
The timer pull model is in place so we can remove the heuristics which try
to guess the best target CPU at enqueue/modification time.
All non pinned timers are queued on the local CPU in the separate storage
and eventually pulled at expiry time to a remote CPU.
Originally-by: Richard Cochran (linutronix GmbH) <richardcochran@...il.com>
Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20240221090548.36600-21-anna-maria@linutronix.de
---
include/linux/timer.h | 14 ++++----------
kernel/time/timer.c | 36 +++++++++++++++---------------------
2 files changed, 19 insertions(+), 31 deletions(-)
diff --git a/include/linux/timer.h b/include/linux/timer.h
index 2be8be6..14a633b 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -36,16 +36,10 @@
* workqueue locking issues. It's not meant for executing random crap
* with interrupts disabled. Abuse is monitored!
*
- * @TIMER_PINNED: A pinned timer will not be affected by any timer
- * placement heuristics (like, NOHZ) and will always expire on the CPU
- * on which the timer was enqueued.
- *
- * Note: Because enqueuing of timers can migrate the timer from one
- * CPU to another, pinned timers are not guaranteed to stay on the
- * initialy selected CPU. They move to the CPU on which the enqueue
- * function is invoked via mod_timer() or add_timer(). If the timer
- * should be placed on a particular CPU, then add_timer_on() has to be
- * used.
+ * @TIMER_PINNED: A pinned timer will always expire on the CPU on which the
+ * timer was enqueued. When a particular CPU is required, add_timer_on()
+ * has to be used. Enqueue via mod_timer() and add_timer() is always done
+ * on the local CPU.
*/
#define TIMER_CPUMASK 0x0003FFFF
#define TIMER_MIGRATING 0x00040000
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 3ed135c..4f4930d 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -635,11 +635,16 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
/*
* We might have to IPI the remote CPU if the base is idle and the
- * timer is not deferrable. If the other CPU is on the way to idle
- * then it can't set base->is_idle as we hold the base lock:
+ * timer is pinned. If it is a non pinned timer, it is only queued
+ * on the remote CPU, when timer was running during queueing. Then
+ * everything is handled by remote CPU anyway. If the other CPU is
+ * on the way to idle then it can't set base->is_idle as we hold
+ * the base lock:
*/
- if (base->is_idle)
+ if (base->is_idle) {
+ WARN_ON_ONCE(!(timer->flags & TIMER_PINNED));
wake_up_nohz_cpu(base->cpu);
+ }
}
/*
@@ -986,17 +991,6 @@ static inline struct timer_base *get_timer_base(u32 tflags)
return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK);
}
-static inline struct timer_base *
-get_target_base(struct timer_base *base, unsigned tflags)
-{
-#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
- if (static_branch_likely(&timers_migration_enabled) &&
- !(tflags & TIMER_PINNED))
- return get_timer_cpu_base(tflags, get_nohz_timer_target());
-#endif
- return get_timer_this_cpu_base(tflags);
-}
-
static inline void __forward_timer_base(struct timer_base *base,
unsigned long basej)
{
@@ -1151,7 +1145,7 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option
if (!ret && (options & MOD_TIMER_PENDING_ONLY))
goto out_unlock;
- new_base = get_target_base(base, timer->flags);
+ new_base = get_timer_this_cpu_base(timer->flags);
if (base != new_base) {
/*
@@ -2297,7 +2291,7 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
* granularity skew (by design).
*/
if (!base_local->is_idle && time_after(nextevt, basej + 1)) {
- base_local->is_idle = base_global->is_idle = true;
+ base_local->is_idle = true;
trace_timer_base_idle(true, base_local->cpu);
}
*idle = base_local->is_idle;
@@ -2363,13 +2357,13 @@ u64 timer_base_try_to_set_idle(unsigned long basej, u64 basem, bool *idle)
void timer_clear_idle(void)
{
/*
- * We do this unlocked. The worst outcome is a remote enqueue sending
- * a pointless IPI, but taking the lock would just make the window for
- * sending the IPI a few instructions smaller for the cost of taking
- * the lock in the exit from idle path.
+ * We do this unlocked. The worst outcome is a remote pinned timer
+ * enqueue sending a pointless IPI, but taking the lock would just
+ * make the window for sending the IPI a few instructions smaller
+ * for the cost of taking the lock in the exit from idle
+ * path. Required for BASE_LOCAL only.
*/
__this_cpu_write(timer_bases[BASE_LOCAL].is_idle, false);
- __this_cpu_write(timer_bases[BASE_GLOBAL].is_idle, false);
trace_timer_base_idle(false, smp_processor_id());
/* Activate without holding the timer_base->lock */
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