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a127d2bcf1
The hrtimer mode of broadcast queues hrtimers in the idle entry
path so as to wakeup cpus in deep idle states. The associated
call graph is :
cpuidle_idle_call()
|____ clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, ....))
|_____tick_broadcast_set_event()
|____clockevents_program_event()
|____bc_set_next()
The hrtimer_{start/cancel} functions call into tracing which uses RCU.
But it is not legal to call into RCU in cpuidle because it is one of the
quiescent states. Hence protect this region with RCU_NONIDLE which informs
RCU that the cpu is momentarily non-idle.
As an aside it is helpful to point out that the clock event device that is
programmed here is not a per-cpu clock device; it is a
pseudo clock device, used by the broadcast framework alone.
The per-cpu clock device programming never goes through bc_set_next().
Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linuxppc-dev@ozlabs.org
Cc: mpe@ellerman.id.au
Cc: tglx@linutronix.de
Link: http://lkml.kernel.org/r/20150318104705.17763.56668.stgit@preeti.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
114 lines
3.0 KiB
C
114 lines
3.0 KiB
C
/*
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* linux/kernel/time/tick-broadcast-hrtimer.c
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* This file emulates a local clock event device
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* via a pseudo clock device.
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*/
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#include <linux/cpu.h>
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#include <linux/err.h>
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#include <linux/hrtimer.h>
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#include <linux/interrupt.h>
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#include <linux/percpu.h>
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#include <linux/profile.h>
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#include <linux/clockchips.h>
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#include <linux/sched.h>
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#include <linux/smp.h>
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#include <linux/module.h>
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#include "tick-internal.h"
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static struct hrtimer bctimer;
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static void bc_set_mode(enum clock_event_mode mode,
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struct clock_event_device *bc)
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{
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switch (mode) {
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case CLOCK_EVT_MODE_SHUTDOWN:
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/*
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* Note, we cannot cancel the timer here as we might
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* run into the following live lock scenario:
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*
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* cpu 0 cpu1
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* lock(broadcast_lock);
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* hrtimer_interrupt()
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* bc_handler()
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* tick_handle_oneshot_broadcast();
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* lock(broadcast_lock);
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* hrtimer_cancel()
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* wait_for_callback()
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*/
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hrtimer_try_to_cancel(&bctimer);
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break;
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default:
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break;
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}
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}
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/*
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* This is called from the guts of the broadcast code when the cpu
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* which is about to enter idle has the earliest broadcast timer event.
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*/
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static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
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{
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int bc_moved;
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/*
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* We try to cancel the timer first. If the callback is on
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* flight on some other cpu then we let it handle it. If we
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* were able to cancel the timer nothing can rearm it as we
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* own broadcast_lock.
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*
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* However we can also be called from the event handler of
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* ce_broadcast_hrtimer itself when it expires. We cannot
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* restart the timer because we are in the callback, but we
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* can set the expiry time and let the callback return
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* HRTIMER_RESTART.
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*
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* Since we are in the idle loop at this point and because
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* hrtimer_{start/cancel} functions call into tracing,
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* calls to these functions must be bound within RCU_NONIDLE.
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*/
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RCU_NONIDLE(bc_moved = (hrtimer_try_to_cancel(&bctimer) >= 0) ?
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!hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED) :
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0);
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if (bc_moved) {
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/* Bind the "device" to the cpu */
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bc->bound_on = smp_processor_id();
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} else if (bc->bound_on == smp_processor_id()) {
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hrtimer_set_expires(&bctimer, expires);
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}
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return 0;
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}
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static struct clock_event_device ce_broadcast_hrtimer = {
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.set_mode = bc_set_mode,
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.set_next_ktime = bc_set_next,
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.features = CLOCK_EVT_FEAT_ONESHOT |
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CLOCK_EVT_FEAT_KTIME |
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CLOCK_EVT_FEAT_HRTIMER,
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.rating = 0,
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.bound_on = -1,
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.min_delta_ns = 1,
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.max_delta_ns = KTIME_MAX,
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.min_delta_ticks = 1,
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.max_delta_ticks = ULONG_MAX,
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.mult = 1,
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.shift = 0,
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.cpumask = cpu_all_mask,
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};
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static enum hrtimer_restart bc_handler(struct hrtimer *t)
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{
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ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
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if (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX)
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return HRTIMER_NORESTART;
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return HRTIMER_RESTART;
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}
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void tick_setup_hrtimer_broadcast(void)
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{
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hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
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bctimer.function = bc_handler;
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clockevents_register_device(&ce_broadcast_hrtimer);
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}
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