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From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, "Will Deacon" <will@kernel.org>,
	"Frederic Weisbecker" <fweisbec@gmail.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Marc Zyngier" <maz@kernel.org>,
	"Lorenzo Colitti" <lorenzo@google.com>,
	"John Stultz" <john.stultz@linaro.org>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Mika Penttilä" <mika.penttila@nextfour.com>,
	kernel-team@android.com
Subject: [PATCH v2 3/5] tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast
Date: Mon, 24 May 2021 23:18:16 +0100	[thread overview]
Message-ID: <20210524221818.15850-4-will@kernel.org> (raw)
In-Reply-To: <20210524221818.15850-1-will@kernel.org>

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@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Lorenzo Colitti <lorenzo@google.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Will Deacon <will@kernel.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


  parent reply	other threads:[~2021-05-24 22:18 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-24 22:18 [PATCH v2 0/5] tick/broadcast: Allow per-cpu timers to be used instead of broadcast Will Deacon
2021-05-24 22:18 ` [PATCH v2 1/5] tick/broadcast: Drop unneeded CONFIG_GENERIC_CLOCKEVENTS_BROADCAST guard Will Deacon
2021-05-31 15:07   ` [tip: timers/core] " tip-bot2 for Will Deacon
2021-05-24 22:18 ` [PATCH v2 2/5] tick/broadcast: Split __tick_broadcast_oneshot_control() into a helper Will Deacon
2021-05-27  7:23   ` Xin Hao
2021-05-27  8:22     ` Will Deacon
2021-05-27 11:35       ` Xin Hao
2021-05-27 11:55         ` Will Deacon
2021-05-27 11:56         ` Will Deacon
2021-05-31 14:29           ` Thomas Gleixner
2021-06-01 12:13             ` Will Deacon
2021-06-01 18:14               ` Thomas Gleixner
2021-05-31 15:06   ` [tip: timers/core] " tip-bot2 for Will Deacon
2021-05-24 22:18 ` Will Deacon [this message]
2021-05-31 15:06   ` [tip: timers/core] tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast tip-bot2 for Will Deacon
2021-05-24 22:18 ` [PATCH v2 4/5] tick/broadcast: Program wakeup timer when entering idle if required Will Deacon
2021-05-31 15:06   ` [tip: timers/core] " tip-bot2 for Will Deacon
2021-05-24 22:18 ` [PATCH v2 5/5] timer_list: Print name of per-cpu wakeup device Will Deacon
2021-05-31 15:06   ` [tip: timers/core] " tip-bot2 for Will Deacon

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