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2bbb6817c0
It is assumed that rcu won't be used once we switch to tickless mode and until we restart the tick. However this is not always true, as in x86-64 where we dereference the idle notifiers after the tick is stopped. To prepare for fixing this, add two new APIs: tick_nohz_idle_enter_norcu() and tick_nohz_idle_exit_norcu(). If no use of RCU is made in the idle loop between tick_nohz_enter_idle() and tick_nohz_exit_idle() calls, the arch must instead call the new *_norcu() version such that the arch doesn't need to call rcu_idle_enter() and rcu_idle_exit(). Otherwise the arch must call tick_nohz_enter_idle() and tick_nohz_exit_idle() and also call explicitly: - rcu_idle_enter() after its last use of RCU before the CPU is put to sleep. - rcu_idle_exit() before the first use of RCU after the CPU is woken up. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Mike Frysinger <vapier@gentoo.org> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: David Miller <davem@davemloft.net> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Russell King <linux@arm.linux.org.uk> Cc: Paul Mackerras <paulus@samba.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
139 lines
3.0 KiB
C
139 lines
3.0 KiB
C
/*
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* Idle daemon for PowerPC. Idle daemon will handle any action
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* that needs to be taken when the system becomes idle.
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*
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* Originally written by Cort Dougan (cort@cs.nmt.edu).
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* Subsequent 32-bit hacking by Tom Rini, Armin Kuster,
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* Paul Mackerras and others.
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*
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* iSeries supported added by Mike Corrigan <mikejc@us.ibm.com>
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*
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* Additional shared processor, SMT, and firmware support
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* Copyright (c) 2003 Dave Engebretsen <engebret@us.ibm.com>
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*
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* 32-bit and 64-bit versions merged by Paul Mackerras <paulus@samba.org>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/smp.h>
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#include <linux/cpu.h>
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#include <linux/sysctl.h>
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#include <linux/tick.h>
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#include <asm/system.h>
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#include <asm/processor.h>
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#include <asm/cputable.h>
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#include <asm/time.h>
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#include <asm/machdep.h>
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#include <asm/smp.h>
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#ifdef CONFIG_HOTPLUG_CPU
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#define cpu_should_die() cpu_is_offline(smp_processor_id())
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#else
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#define cpu_should_die() 0
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#endif
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static int __init powersave_off(char *arg)
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{
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ppc_md.power_save = NULL;
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return 0;
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}
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__setup("powersave=off", powersave_off);
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/*
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* The body of the idle task.
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*/
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void cpu_idle(void)
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{
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if (ppc_md.idle_loop)
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ppc_md.idle_loop(); /* doesn't return */
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set_thread_flag(TIF_POLLING_NRFLAG);
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while (1) {
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tick_nohz_idle_enter_norcu();
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while (!need_resched() && !cpu_should_die()) {
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ppc64_runlatch_off();
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if (ppc_md.power_save) {
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clear_thread_flag(TIF_POLLING_NRFLAG);
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/*
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* smp_mb is so clearing of TIF_POLLING_NRFLAG
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* is ordered w.r.t. need_resched() test.
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*/
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smp_mb();
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local_irq_disable();
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/* Don't trace irqs off for idle */
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stop_critical_timings();
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/* check again after disabling irqs */
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if (!need_resched() && !cpu_should_die())
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ppc_md.power_save();
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start_critical_timings();
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local_irq_enable();
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set_thread_flag(TIF_POLLING_NRFLAG);
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} else {
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/*
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* Go into low thread priority and possibly
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* low power mode.
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*/
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HMT_low();
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HMT_very_low();
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}
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}
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HMT_medium();
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ppc64_runlatch_on();
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tick_nohz_idle_exit_norcu();
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preempt_enable_no_resched();
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if (cpu_should_die())
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cpu_die();
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schedule();
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preempt_disable();
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}
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}
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int powersave_nap;
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#ifdef CONFIG_SYSCTL
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/*
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* Register the sysctl to set/clear powersave_nap.
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*/
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static ctl_table powersave_nap_ctl_table[]={
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{
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.procname = "powersave-nap",
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.data = &powersave_nap,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec,
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},
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{}
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};
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static ctl_table powersave_nap_sysctl_root[] = {
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{
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.procname = "kernel",
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.mode = 0555,
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.child = powersave_nap_ctl_table,
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},
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{}
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};
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static int __init
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register_powersave_nap_sysctl(void)
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{
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register_sysctl_table(powersave_nap_sysctl_root);
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return 0;
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}
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__initcall(register_powersave_nap_sysctl);
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#endif
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