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Date: Mon, 24 May 2021 23:18:16 +0100
From: Will Deacon <will@...nel.org>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Marc Zyngier <maz@...nel.org>,
Lorenzo Colitti <lorenzo@...gle.com>,
John Stultz <john.stultz@...aro.org>,
Stephen Boyd <sboyd@...nel.org>,
Mika Penttilä <mika.penttila@...tfour.com>,
kernel-team@...roid.com
Subject: [PATCH v2 3/5] tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast
Some SoCs have two per-cpu timer implementations where the timer with
the higher rating stops in deep idle (i.e. suffers from
CLOCK_EVT_FEAT_C3STOP) but is otherwise preferable to the timer with the
lower rating. In such a design, we rely on a global broadcast timer and
IPIs to wake up from deep idle states.
To avoid the reliance on a global broadcast timer and also to reduce the
overhead associated with the IPI wakeups, extend
tick_install_broadcast_device() to manage per-cpu wakeup timers
separately from the broadcast device.
For now, these timers remain unused.
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Lorenzo Colitti <lorenzo@...gle.com>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Stephen Boyd <sboyd@...nel.org>
Signed-off-by: Will Deacon <will@...nel.org>
---
kernel/time/tick-broadcast.c | 59 +++++++++++++++++++++++++++++++++++-
kernel/time/tick-common.c | 2 +-
kernel/time/tick-internal.h | 4 +--
3 files changed, 61 insertions(+), 4 deletions(-)
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index f3f2f4ba4321..0e9e06d6cc5c 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -33,6 +33,8 @@ static int tick_broadcast_forced;
static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(tick_broadcast_lock);
#ifdef CONFIG_TICK_ONESHOT
+static DEFINE_PER_CPU(struct clock_event_device *, tick_oneshot_wakeup_device);
+
static void tick_broadcast_setup_oneshot(struct clock_event_device *bc);
static void tick_broadcast_clear_oneshot(int cpu);
static void tick_resume_broadcast_oneshot(struct clock_event_device *bc);
@@ -88,13 +90,65 @@ static bool tick_check_broadcast_device(struct clock_event_device *curdev,
return !curdev || newdev->rating > curdev->rating;
}
+#ifdef CONFIG_TICK_ONESHOT
+static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu)
+{
+ return per_cpu(tick_oneshot_wakeup_device, cpu);
+}
+
+static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev,
+ int cpu)
+{
+ struct clock_event_device *curdev = tick_get_oneshot_wakeup_device(cpu);
+
+ if (!newdev)
+ goto set_device;
+
+ if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) ||
+ (newdev->features & CLOCK_EVT_FEAT_C3STOP))
+ return false;
+
+ if (!(newdev->features & CLOCK_EVT_FEAT_PERCPU) ||
+ !(newdev->features & CLOCK_EVT_FEAT_ONESHOT))
+ return false;
+
+ if (!cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
+ return false;
+
+ if (curdev && newdev->rating <= curdev->rating)
+ return false;
+
+ if (!try_module_get(newdev->owner))
+ return false;
+
+set_device:
+ clockevents_exchange_device(curdev, newdev);
+ per_cpu(tick_oneshot_wakeup_device, cpu) = newdev;
+ return true;
+}
+#else
+static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu)
+{
+ return NULL;
+}
+
+static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev,
+ int cpu)
+{
+ return false;
+}
+#endif
+
/*
* Conditionally install/replace broadcast device
*/
-void tick_install_broadcast_device(struct clock_event_device *dev)
+void tick_install_broadcast_device(struct clock_event_device *dev, int cpu)
{
struct clock_event_device *cur = tick_broadcast_device.evtdev;
+ if (tick_set_oneshot_wakeup_device(dev, cpu))
+ return;
+
if (!tick_check_broadcast_device(cur, dev))
return;
@@ -996,6 +1050,9 @@ void hotplug_cpu__broadcast_tick_pull(int deadcpu)
*/
static void tick_broadcast_oneshot_offline(unsigned int cpu)
{
+ if (tick_get_oneshot_wakeup_device(cpu))
+ tick_set_oneshot_wakeup_device(NULL, cpu);
+
/*
* Clear the broadcast masks for the dead cpu, but do not stop
* the broadcast device!
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index e15bc0ef1912..d663249652ef 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -373,7 +373,7 @@ void tick_check_new_device(struct clock_event_device *newdev)
/*
* Can the new device be used as a broadcast device ?
*/
- tick_install_broadcast_device(newdev);
+ tick_install_broadcast_device(newdev, cpu);
}
/**
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 7a981c9e87a4..30c89639e305 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -61,7 +61,7 @@ extern ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt);
/* Broadcasting support */
# ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
extern int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu);
-extern void tick_install_broadcast_device(struct clock_event_device *dev);
+extern void tick_install_broadcast_device(struct clock_event_device *dev, int cpu);
extern int tick_is_broadcast_device(struct clock_event_device *dev);
extern void tick_suspend_broadcast(void);
extern void tick_resume_broadcast(void);
@@ -72,7 +72,7 @@ extern int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq);
extern struct tick_device *tick_get_broadcast_device(void);
extern struct cpumask *tick_get_broadcast_mask(void);
# else /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST: */
-static inline void tick_install_broadcast_device(struct clock_event_device *dev) { }
+static inline void tick_install_broadcast_device(struct clock_event_device *dev, int cpu) { }
static inline int tick_is_broadcast_device(struct clock_event_device *dev) { return 0; }
static inline int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu) { return 0; }
static inline void tick_do_periodic_broadcast(struct clock_event_device *d) { }
--
2.31.1.818.g46aad6cb9e-goog
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