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, selecting the higher rated devices relies 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.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210524221818.15850-4-will@kernel.org

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index f3f2f4ba432193030c3c1a0ba5a8d95a927313cc..0e9e06d6cc5cb97ab9bcbb383314fd0140f7969a 100644 (file)
--- 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 e15bc0ef191282561eaae1e9c91e851d692e54b6..d663249652efb6c63e7c0c5d97378324da191295 100644 (file)
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -373,7 +373,7 @@ out_bc:
        /*
         * 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 7a981c9e87a4aafa8dcbca51d26f541d44bf969b..30c89639e305fce99aaf2340cb2e9f3a4328e84c 100644 (file)
--- 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) { }