linux/kernel/time/tick-broadcast-hrtimer.c

107 lines
2.7 KiB
C
Raw Normal View History

tick: Introduce hrtimer based broadcast On some architectures, in certain CPU deep idle states the local timers stop. An external clock device is used to wakeup these CPUs. The kernel support for the wakeup of these CPUs is provided by the tick broadcast framework by using the external clock device as the wakeup source. However not all implementations of architectures provide such an external clock device. This patch includes support in the broadcast framework to handle the wakeup of the CPUs in deep idle states on such systems by queuing a hrtimer on one of the CPUs, which is meant to handle the wakeup of CPUs in deep idle states. This patchset introduces a pseudo clock device which can be registered by the archs as tick_broadcast_device in the absence of a real external clock device. Once registered, the broadcast framework will work as is for these architectures as long as the archs take care of the BROADCAST_ENTER notification failing for one of the CPUs. This CPU is made the stand by CPU to handle wakeup of the CPUs in deep idle and it *must not enter deep idle states*. The CPU with the earliest wakeup is chosen to be this CPU. Hence this way the stand by CPU dynamically moves around and so does the hrtimer which is queued to trigger at the next earliest wakeup time. This is consistent with the case where an external clock device is present. The smp affinity of this clock device is set to the CPU with the earliest wakeup. This patchset handles the hotplug of the stand by CPU as well by moving the hrtimer on to the CPU handling the CPU_DEAD notification. Originally-from: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Cc: deepthi@linux.vnet.ibm.com Cc: paulmck@linux.vnet.ibm.com Cc: fweisbec@gmail.com Cc: paulus@samba.org Cc: srivatsa.bhat@linux.vnet.ibm.com Cc: svaidy@linux.vnet.ibm.com Cc: peterz@infradead.org Cc: benh@kernel.crashing.org Cc: rafael.j.wysocki@intel.com Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20140207080632.17187.80532.stgit@preeti.in.ibm.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2014-02-07 08:06:32 +00:00
/*
* linux/kernel/time/tick-broadcast-hrtimer.c
* This file emulates a local clock event device
* via a pseudo clock device.
*/
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/clockchips.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/module.h>
#include "tick-internal.h"
static struct hrtimer bctimer;
static void bc_set_mode(enum clock_event_mode mode,
struct clock_event_device *bc)
{
switch (mode) {
case CLOCK_EVT_MODE_SHUTDOWN:
/*
* Note, we cannot cancel the timer here as we might
* run into the following live lock scenario:
*
* cpu 0 cpu1
* lock(broadcast_lock);
* hrtimer_interrupt()
* bc_handler()
* tick_handle_oneshot_broadcast();
* lock(broadcast_lock);
* hrtimer_cancel()
* wait_for_callback()
*/
hrtimer_try_to_cancel(&bctimer);
break;
default:
break;
}
}
/*
* This is called from the guts of the broadcast code when the cpu
* which is about to enter idle has the earliest broadcast timer event.
*/
static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
{
/*
* We try to cancel the timer first. If the callback is on
* flight on some other cpu then we let it handle it. If we
* were able to cancel the timer nothing can rearm it as we
* own broadcast_lock.
*
* However we can also be called from the event handler of
* ce_broadcast_hrtimer itself when it expires. We cannot
* restart the timer because we are in the callback, but we
* can set the expiry time and let the callback return
* HRTIMER_RESTART.
*/
if (hrtimer_try_to_cancel(&bctimer) >= 0) {
hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
/* Bind the "device" to the cpu */
bc->bound_on = smp_processor_id();
} else if (bc->bound_on == smp_processor_id()) {
hrtimer_set_expires(&bctimer, expires);
}
return 0;
}
static struct clock_event_device ce_broadcast_hrtimer = {
.set_mode = bc_set_mode,
.set_next_ktime = bc_set_next,
.features = CLOCK_EVT_FEAT_ONESHOT |
CLOCK_EVT_FEAT_KTIME |
CLOCK_EVT_FEAT_HRTIMER,
.rating = 0,
.bound_on = -1,
.min_delta_ns = 1,
.max_delta_ns = KTIME_MAX,
.min_delta_ticks = 1,
.max_delta_ticks = ULONG_MAX,
tick: Introduce hrtimer based broadcast On some architectures, in certain CPU deep idle states the local timers stop. An external clock device is used to wakeup these CPUs. The kernel support for the wakeup of these CPUs is provided by the tick broadcast framework by using the external clock device as the wakeup source. However not all implementations of architectures provide such an external clock device. This patch includes support in the broadcast framework to handle the wakeup of the CPUs in deep idle states on such systems by queuing a hrtimer on one of the CPUs, which is meant to handle the wakeup of CPUs in deep idle states. This patchset introduces a pseudo clock device which can be registered by the archs as tick_broadcast_device in the absence of a real external clock device. Once registered, the broadcast framework will work as is for these architectures as long as the archs take care of the BROADCAST_ENTER notification failing for one of the CPUs. This CPU is made the stand by CPU to handle wakeup of the CPUs in deep idle and it *must not enter deep idle states*. The CPU with the earliest wakeup is chosen to be this CPU. Hence this way the stand by CPU dynamically moves around and so does the hrtimer which is queued to trigger at the next earliest wakeup time. This is consistent with the case where an external clock device is present. The smp affinity of this clock device is set to the CPU with the earliest wakeup. This patchset handles the hotplug of the stand by CPU as well by moving the hrtimer on to the CPU handling the CPU_DEAD notification. Originally-from: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Cc: deepthi@linux.vnet.ibm.com Cc: paulmck@linux.vnet.ibm.com Cc: fweisbec@gmail.com Cc: paulus@samba.org Cc: srivatsa.bhat@linux.vnet.ibm.com Cc: svaidy@linux.vnet.ibm.com Cc: peterz@infradead.org Cc: benh@kernel.crashing.org Cc: rafael.j.wysocki@intel.com Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20140207080632.17187.80532.stgit@preeti.in.ibm.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2014-02-07 08:06:32 +00:00
.mult = 1,
.shift = 0,
.cpumask = cpu_all_mask,
};
static enum hrtimer_restart bc_handler(struct hrtimer *t)
{
ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
if (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX)
return HRTIMER_NORESTART;
return HRTIMER_RESTART;
}
void tick_setup_hrtimer_broadcast(void)
{
hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
bctimer.function = bc_handler;
clockevents_register_device(&ce_broadcast_hrtimer);
}